Introduction

STEM Education has been at the forefront of curriculum reform efforts and guidelines for multiple purposes, ranging from knowledge and skills development to goals related to equity and inclusion (European Commission, 2022). STEM education research findings showcase that teachers lack an understanding of connections between STEM disciplines as well as pedagogical approaches to teaching STEM in real-life situations (Kurup et al., 2019). At the same time, reform documents (e.g. European Commission, 2022; National Research Council [NRC], 2014) call for the importance of making intentional and explicit connections within and across disciplines for the purpose of equipping students to engage with complex real-world problems that are interdisciplinary in nature. Hence, specially designed Professional Development (PD) programmes are needed in order to support teachers in gaining the knowledge and skills needed to design and enact integrated STEM instructional materials (Al Salami et al., 2017).

For the purpose of the study reported in the manuscript, we define integrated STEM as a “teaching approach that integrates content and skills specific to Science, Technology, Engineering & Mathematics” (Martín‐Páez et al., 2019, p. 17). Hence, STEM is regarded by definition as an integrative approach. We draw on Roehrig et al.’s (2021) conceptual framework for integrated STEM, since it draws upon a literature review in STEM and proposes seven key characteristics for STEM which we consider representative of what should be expected in integrated STEM approaches: 1) Focus on real-world problems, 2) Engagement in engineering design, 3) Context integration, 4) Content integration, 5) Engagement in authentic STEM practices, 6) 21st-century skills, and 7) STEM careers. In order to analyse the common ground among disciplines in terms of concepts/methods/artefacts/questions that teachers identify when designing integrated STEM teaching, we use the boundary objects framework (Akkerman & Bakker, 2011).

Previous studies have shown divergencies in teachers’ practice when implementing STEM (Wang et al., 2011), as well as divergencies in their perceptions of what is STEM (Ring et al., 2017). However, little attention has been paid to the unique epistemologies of the constituent disciplines of STEM, the barriers and affinities/relations among them, as well as the ways in which these could be overcome through a collaborative interdisciplinary setting (Millar, 2020).

STEM disciplines originate from two major traditions: the ‘natural’/ ‘pure’ sciences (science, mathematics) and the ‘design’/ ‘applied’ sciences (technology, engineering) (Becher & Trowler, 2001; Nathan et al., 2013). One characteristic difference is that science and mathematics mainly represent ways of knowing and interpreting the world, while technology and engineering mainly focus on physical and non-physical forms of design (Quinn et al., 2020). Since STEM refers to the integration of disciplines with much different epistemologies, it is important to shed light on their peculiarities and traits. Even more importantly, if STEM is to be applied in schools, it is important to investigate the instructional design practices of teachers coming from different disciplinary backgrounds. Our previous work has demonstrated differences in teachers’ views on STEM at the disciplinary level, as for example, the ways that teachers from natural and design sciences implement engineering design or the real-world problem contextualisation of the topic (Nipyrakis et al., 2024). Differences also appear in the design of STEM artefacts, since most teachers tend to take on parts that are closer to their disciplinary expertise and orientation (Nipyrakis, 2023).

Moreover, research shows that collaboration between agents of diverse expertise can assist in the identification of the similarities and differences among different communities, as well as the understanding of the connections and the relevance of concepts (Couso, 2016; Kähkönen et al., 2016). Therefore, for the design of this study, we adopted a learning community approach which is a participatory approach based on enquiry, reflection and collaborative research and development of curriculum (Couso, 2016). In our study, it was realised as a small-group setting in which teachers from diverse disciplines collaborate on a joint task through reflexive dialogue in an inquiry stance. For the purpose of this study, a group of teachers of diverse S-T-E-M backgrounds collaborated in the design and development of STEM teaching material, i.e. lesson plans and physical/digital artefacts. This study focused solely on the design of STEM lesson plans.

RQ1: How do S-T-E-M teachers develop STEM teaching material?

  • 1.1) What key characteristics of integrated STEM do teachers take into consideration and in what ways?

  • 1.2) What order do teachers follow in their sequence of teaching activities?

RQ2: What disciplinary and interdisciplinary aspects do S-T-E-M teachers identify and incorporate when designing STEM lesson plans?

The findings of this case study aim to shed light on patterns and nuances in designing STEM teaching material by the teachers which can inform the design and development of integrated STEM PD programmes for teachers. Moreover, the cross-examination of the design practices at the disciplinary level can contribute to the literature gap about the challenges that teachers face when attempting to work on interdisciplinary tasks.

Literature Review

Integrated STEM

STEM integration is defined as “working in the context of complex phenomena or situations that require students to use knowledge and skills from multiple disciplines” (NRC, 2014, p. 52). However, integrating disciplines is a complex process that could be implemented in many different ways, which justifies the use of a generic definition, such as the Martín‐Páez et al.’s (2019) definition which was used in our study. Four main levels of integration are: a) disciplinary, in which disciplines are being taught in silos; therefore integration is missing, b) multidisciplinary, in which disciplines are been presented in an encyclopedic, sequential or coordinated way and connected only through a common theme (English, 2016; Klein, 2017), c) interdisciplinary, in which “knowledge and modes of thinking from two or more disciplines are integrated to produce a cognitive advancement that would have been impossible or unlikely through single disciplinary means” (Crujeiras-Pérez & Jiménez-Alexandre, 2019, p. 31), and iv) transdisciplinary, in which a common system of axioms transcends the scope of disciplinary worldviews through an overarching synthesis (Klein, 2017); therefore it is considered broader and exogenous (Alvargonzález, 2011).

Several models have been proposed in the literature for integrated STEM, coming from both theoretical and empirical bases. Bybee (2013) suggested nine theoretical models through schemes and analogies representing the interrelations among disciplines. Ortiz-Revilla et al. (2022) presented Laudan’s triadic network of three domains: theories, methods and aims as a model for integrated STEM, based on Laudan’s epistemology of problems as a backbone for STEM. Quinn et al. (2020) suggested the Nature of Engineering as a congruent model for the Nature of STEM. On the other side, Ring et al. (2017) based on empirical data from teachers’ reflections on what is STEM in order to identify eight main models of STEM.

A literature review on STEM education by Roehrig et al. (2021) has resulted in seven key characteristics of integrated STEM. In specific, the key characteristics are: 1) Focus on real-world problems or contexts or authentic problems in order to engage and motivate students, while careful attention should be given to engaging students from underrepresented groups in STEM due to gender, race, etc. 2) Engagement in engineering design. It is recommended that students engage with engineering design challenges to systematically and iteratively design solutions, understand and address the criteria and constraints of a problem, as well as related ethical and societal issues. 3) Context integration, explicit integration between the problem context and the related STEM content goals, as well as the socio-historical-political context of the problems. 4) Content integration, the explicit identification of the connections among STEM disciplines. 5) Engagement with STEM practices, such as data practices, argumentation, identifying multiple solutions, epistemic agency, etc. 6) 21st-century skills, which in the present study relate to: Critical thinking, Creativity, Collaboration and Communication, which were deemed the core skills (Dare et al., 2021). 7) Promotion of STEM careers, through the engagement in the authentic work of professionals and in understanding and activating the predictors that formulate STEM identities, such as recognition, interest, competence and performance (Avraamidou, 2022; Drymiotou et al., 2021; Munfaridah et al., 2022).

Regardless of the work on conceptualizing STEM theoretically, informed interdisciplinary curricula are scarce (Millar, 2019). Hence, it becomes imperative to analyse teachers’ STEM lesson plans in order to explore what teachers think about integrated STEM instruction (Pleasants et al., 2021), and to examine whether STEM policy recommendations can actually work at the classroom level (Kim & Bolger, 2017).

Designing STEM lesson plans is a process which, albeit challenging, can positively affect teachers’ attitudes towards STEM (Kim & Bolger, 2017). Teachers’ STEM lesson planning can improve through incorporating key features such as dealing with uncertainty, failure and contingencies (Leung, 2019). At the disciplinary level, Bergsten and Frejd (2019) showed that mathematics teachers’ lesson plans mostly integrate science, while programming is used as a tool. Furthermore, in Pleasants’ et al.s (2021) study, elementary teachers tended to connect engineering and science in a swallow or theme-based way, while they included engineering design activities at the end of their lesson plans. However, a cross-comparison of STEM lesson planning practices of all S-T-E-M disciplinary agents is missing. In this light, the findings of this study contribute unique insights to the knowledge base in terms of examination of how the S-T-E-M disciplinary backgrounds affect the development of STEM lesson planning, by inspecting teachers’ preferences, peculiarities and challenges in implementing STEM characteristics.

Disciplinary Boundaries and Boundary Crossing

The construct of a discipline relates to a “body of knowledge that has been historically organised to be taught and learnt”, which supports the development of epistemic skills (e.g. modelling, explaining, arguing, etc.) which take different forms in different disciplines (Barelli et al., 2022).

Importantly, making interconnections among disciplines prerequires an understanding of definitions of what each STEM discipline represents, as the ones proposed by NRC (2014). Although in some cases definitions may become trivial, in the case of technology and engineering the ‘boundaries’ are blurred. Particularly, engineering is related more to the application of scientific and mathematical knowledge, while the main differentiation from technology is that engineering emphasises more to design (Murphy et al., 2015).

Hence, each discipline includes both knowledge and skills elements. Particularly, UNESCO defined knowledge as “the ability to recall and present information that is described using learning outcomes”, and skills as “the ability to do in context that is described using learning outcomes” (Keevy & Chakroun, 2015, pp. 157–158).

As regards making interconnections among disciplines, which is the goal in integrated STEM, it is crucial that interconnections are made explicitly, since students may not identify and make them spontaneously by themselves (NRC, 2014; Roehrig et al., 2021). The boundary objects framework has been proposed in order to identify interactions and the type of interactions among disciplines (Barelli et al., 2022), hence, assisting in highlighting interdisciplinarity in the phenomena. Specifically, implementing boundary objects can help orient the discussion on specific concepts, processes, etc. in which two or more disciplines interconnect, and can make integration explicit.

Akkerman and Bakker (2011) define boundaries between disciplines as “a sociocultural difference leading to discontinuity in action or interaction”, while boundary crossing is “a person’s transitions and interactions across different sites” (p.133). Notably, the term ‘boundary’ does not refer to ‘edges’, but rather to a shared space (Star, 2010). This process is been facilitated with the use of boundary objects, i.e. concepts, methods/techniques, artefacts or questions/justifications that have a dual and ‘unspecified’ nature: on the one hand they enact the boundaries by addressing and articulating meanings and perspectives (multivoicedness) of various intersecting worlds, and on the other hand these objects move beyond the boundary in that they have an unspecified quality of their own (Akkerman & Bakker, 2011; Barelli et al., 2022). Boundary objects have been implemented in a wide variety of contexts (Lundgren, 2021). Some examples are modelling and graphs, complexity in climate change, parabolic motion, coding/decoding in cryptography (Nipyrakis et al., 2023), sustainability and resilience in environmental studies (Lundgren, 2021).

Drawing upon this knowledge base, our purpose was to examine the STEM characteristics that teachers incorporate in their developed lesson plans, and the interconnections among disciplines that they implement. Furthermore, analysing how teachers’ disciplinary backgrounds affect their design practices will shed light on their preferences and barriers at the disciplinary level.

Methods

Research Design and Context of the study

This study was implemented as a case study approach (Cohen et al., 2009). Specifically, findings from teachers in all learning communities were aggregated in order to identify general patterns in the design of STEM teaching material in relation to teachers’ disciplinary backgrounds.

The study was carried out during a 7-month-long PD programme that was co-designed by the academic institution in collaboration with regional educational stakeholders. A convenient sample of 26 in-service secondary teachers (10 science teachers, 5 technology teachers, 6 engineering teachers and 5 mathematics teachers; 14 of them female and 12 male) volunteered to participate in the PD programme after being informed and invited by the regional stakeholders. Participants’ prior teaching and STEM experience varied and is depicted in the supplemental material. Age of the participants varied, while the socioeconomic background was typical South European.

During the PD programme, the teachers were called upon to design and develop STEM teaching material, and subsequently implement them in classrooms. The topic of the PD programme was chosen to be NanoScience-NanoTechnology (NST) due to its interdisciplinary nature (Kähkönen et al., 2016). Common topics of NST revolve around size-dependent properties of materials, self-assembly, etc. The PD programme, as shown in Table 1, consisted of 13 sessions in three phases: a) a training phase on the topic of NST and integrated STEM principles, b) a phase of designing and developing STEM teacher material, i.e. individual lesson plans and group artefacts, and c) an implementation phase, in which teachers used the developed material for school teaching.

Table 1 The STEM PD Programme
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During the design and development phase (b), the teachers were divided into 4 Learning Communities (LC), in which there was at least one representative coming from each S-T-E-M discipline. Each LC group was called upon to collaboratively design and develop a joint STEM module, e.g. a greenhouse with NST-based materials and renewables. Following that, each teacher was asked to design his/her individual lesson plan in the context of the joint STEM module, based on his/her own preferences. The meetings were held using a mixed modality, incorporating an online communication platform. The platform hosted the synchronous group meetings, a files repository, and facilitated asynchronous communication through an online forum per LC group.

Data Collection

During the second main phase of the programme (before session 11), teachers were called upon to deliver their individual STEM lesson plans related to the group-developed STEM module. In sessions 11 and 12, teachers presented their lesson plans, reflectively discussed in the LC, and were given the chance to further revise them in two iterations after the LC meetings. The present study analysed teachers’ STEM lesson plans, both in their final form and in previous versions. In specific, data collection includes a) teachers’ STEM lesson plans and b) transcribed LC discussions where they presented and reflected on their lesson plans. The LC meetings lasted approximately 75 min each. Teachers’ lesson plans were developed based on the use of a template for designing interdisciplinary teaching modules which was developed and used by STEM academics through a partnership of five academic institutions in the EU project IDENTITIES (www.identitiesproject.eu).

Data Analysis

RQ1) S-T-E-M Teachers’ Lesson Plans

The teaching material was analysed qualitatively through a line-by-line content analysis approach (Mayring, 2015), and through a combination of deductive and inductive coding techniques. In the first phase, the lesson plans were analysed in regard to which of the seven key characteristics of Integrated STEM were included, by identifying related themes in the lesson plan descriptions. Themes were non-overlapping excerpts in which adequate information related to one of the 7 characteristics became apparent. Inductively-made criteria were kept both for the coding of themes as well as the categorisation of themes in each STEM characteristic. The 7 key characteristics of Integrated STEM, as they are described in Roehrig et al.’s (2021) conceptual framework were used deductively in order to taxonomise the codified themes that appeared from the analysis of teachers’ lesson plans. Therefore, a codebook was created of codes that appertain to each one of the 7 key characteristics of STEM. The coding scheme was developed by the first author who first tested it by coding 25% of the lesson plans. Following that, the second and third author coded independently the same number of lesson plans and they then discussed their analysis. Disagreements were resolved through various meaning negotiations until consensus was reached and the coding scheme was then finalised and applied across all lesson plans. Following that, the coded themes were inspected qualitatively in order to identify the main patterns in each characteristic, based on the frequency of the themes and perceived importance.

Additionally, teachers’ oral descriptions of their lesson plans were analysed in order to a) triangulate the findings from the first analysis phase and increase concurrent validity (Cohen et al., 2009), b) to add clarifications on ambiguous points in the lesson plans, and c) to include adjustments and additions that they orally described or decided to include at the final form of their teaching material in comparison with their lesson plan descriptions. A final matrix of patterns in each key characteristic was made based on both phases of the analysis.

Moreover, in order to analyse the sequence of the teaching activities, a matrix was created with brief descriptions of the teaching activities that each teacher chose to implement. In specific, a) data were reduced through brief descriptions, b) the emerging patterns were identified and continuously compared by using constant comparative method (Cohen et al., 2009), c) the process was repeated until saturation was reached, i.e. no more variation occurred.

RQ2) Disciplinary and Interdisciplinary Analysis

The following set of three questions in the STEM template were related to disciplinary and interdisciplinary analysis. The aim of these questions was to foster the identification and elaboration of disciplinary and interdisciplinary aspects in the lesson plans from the teachers.

  1. 2.1)

    What knowledge and skills related to [discipline] do you consider relevant in the teaching material? The analysis unit used is the disciplinary element. A disciplinary element was defined as any piece of information related to knowledge or skills identified by the teachers and taxonomised specifically in each STEM discipline. Disciplines definitions were derived from NRC (2014), while the analysis was made deductively. Furthermore, each disciplinary element was also codified as knowledge or skills, according to UNESCO definitions (Keevy & Chakroun, 2015), while the European Qualifications Framework (EQF) as described in Hoffmann et al. (2010) was also used for clarification. A frequencies matrix of the coded disciplinary elements was made.

  2. 2.2)

    Are there any interconnections between disciplines in the designed teaching module? If yes, describe which are they. The analysis unit used in this part was the interdisciplinary element. An interdisciplinary element was defined as a domain of interconnection between disciplines, in which the interaction and the disciplines involved are stated in an explicit way. Teachers’ responses to the aforementioned lesson plan question were qualitatively codified in relation to whether the interconnection was actually made explicit or not as well as which STEM disciplines are involved in this interaction. Moreover, teachers’ oral descriptions during the LC meetings were also used in order to triangulate the previous analysis of the lesson plans and to include any additional interdisciplinary elements stated by the teachers. The overall results of the coded interdisciplinary elements were organised in a frequency matrix.

  3. 2.3)

    Are there any concepts/phenomena/applications in the teaching module that could not be adequately taught under a unidisciplinary approach? Which are they? In this question, teachers were called upon to identify specific ‘objects’ that require an interdisciplinary teaching approach, since they may belong in various disciplines, which we could characterise as boundary objects. For the analysis of these boundary objects deductive analysis was used, based on the boundary objects categories a) concepts, b) objects/artefacts, c) methods/techniques and d) questions-justifications, suggested by a group of experts in the IDENTITIES project (www.identitiesproject.eu). A matrix was used in order to demonstrate the results and make cross-comparisons among categories.

Findings

RQ1: How do S-T-E-M Teachers Develop STEM Teaching Material?

An overview of the coded themes per key STEM characteristic for each individual teacher, as depicted in Table 2, revealed quite a few discrepancies in the characteristics that each teacher focuses on. For example, some participants stressed the importance of cultivating 21st-century skills and STEM practices, while others emphasised engineering design. Also, divergence in the total duration of the planned STEM teaching appeared, since some teachers planned a teaching sequence of 2 didactic hours, while others proposed a project-like course of up to 15 h, which resulted in a greater number of coded themes. The arising main patterns are discussed as follows.

Table 2 Coded Themes per Individual Teacher
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  1. 1)

    Focus on real-world problems: The majority of participants did implement a real-world context to their lesson plans. However, in 6 cases, reference to the real-world phenomenon was limited or absent. Notably, 5 of these 6 teachers were coming from the ‘design’ sciences (4 engineering and 1 technology), who gave extensive focus on the technical part, e.g. programming the prototype and hence, neglected the real-world context. Other main patterns identified: a) 8 teachers implemented a real-world phenomenon mostly as a theme, without actively problematising students about it, e.g. references about green energy in a ‘smart’ greenhouse topic, b) 4 teachers used several inquiry questions (e.g. variable testing about factors that affect plant development in a greenhouse) without a general coherent relevance on a problem, c) 4 teachers (3 science and 1 technology teacher) referred to a problem but only to a specific lesson plan part/activity while d) 5 teachers (3 science and 2 mathematics teachers) used an open problem related to all lesson plan activities, e.g. fire risk assessment, or greenhouse effect.

  2. 2)

    Engagement in Engineering Design: only 5 teachers planned the construction of the LC team-developed artefact (2 of them with the assistance of a peer teacher), while 11 teachers planned the construction of minor artefacts/parts of it. On the contrary, 8 teachers planned to just use the developed artefact for teaching (e.g. solely for data collection), and 6 teachers (5 of them coming from natural sciences) only demonstrated it to the students, without paying attention to the engineering design process.

  3. 3)

    Context integration: all participants framed their planned activities (or part of them) to STEM content knowledge. 14 of them also implemented socioscientific contexts, (e.g. related to environmental issues, consequences from intervening in human DNA etc.), while 4 of them included elements from the history of science/historical contexts.

  4. 4)

    Content integration: only 5 teachers planned explicit activities about the integration of the disciplines or references to interdisciplinarity, etc., while 18 teachers included activities in which several disciplines were involved, but integration appears rather implicitly.

  5. 5)

    STEM practices: teachers implemented several authentic STEM practices, such as modelling phenomena (n = 16), formal experimentation (n = 8), testing a prototype in order to improve it (n = 6), data practices (n = 10), conduct of a literature/internet research by students (n = 5), epistemic agency activities in general (n = 17), brainstorming (n = 9), coding (n = 14) e.g. a motor or a sensor, etc.

  6. 6)

    twenty-first century skills: the study focused on analysing critical thinking, creativity, collaboration and communication. Regarding critical thinking, several elements were identified in the lesson plans, such as the ability to compare results, to evaluate the feasibility of solutions, to identify the necessity or the importance of that in the field, to compare the simulated results with the experimental ones, to identify the interdependence of variables, etc. Regarding creativity, 2 teachers implemented an activity of designing the prototype, while 1 teacher asked the students to make an artistic dissemination exhibit, like a collage. Many teachers (n = 11) designed collaboration activities in which the students would work in small groups, while 1 teacher facilitated the collaboration between two different classes of students. In terms of communication, 4 teachers also assigned students presentation sessions in the class (e.g. presenting the artefact), while there were references about the language used and the user-friendliness of the digital software.

  7. 7)

    STEM careers: only 4 teachers made reference to STEM careers. In specific, they included aspects about related jobs, entrepreneurship and using innovative technologies, and demonstration of the work of professional scientists.

Sequence and Type of the Activities

Analysing the sequence of the activities that the participants designed in their lesson plans, five common patterns appeared which are described in Table 3.

Table 3 Sequence and Type of the Activities
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Consequently, we can see that teachers followed different patterns regarding their lesson plans. Interestingly, we could infer that teachers’ epistemological background may well have affected the pattern they followed. Particularly, most teachers coming from natural sciences followed a more ‘traditional/theoretical approach’, by starting with the theory and the phenomena explained before they moved to the applications. On the contrary, teachers with a design sciences orientation tended to start by engaging students with the artefact and then with the theory beneath − or even engaging exclusively with the artefact, which is deemed to assimilate a more ‘technical’/’applied’ epistemological orientation. Moreover, a number of natural sciences teachers gave central attention to understanding and answering the main problem/theme, which was considered to be a trait of a natural science epistemology. Finally, some science teachers assimilated their own disciplinary practices in STEM such as experimentation.

RQ2: What Disciplinary and Interdisciplinary Aspects do Teachers Identify and Incorporate in their Lesson Plans?

Disciplinary Analysis

Figure 1 provides an overview of the disciplinary elements identified by teachers in their lesson plans in relation to the disciplinary background of the teachers who identified them. From what we can observe at first glance here is something that we should rather expect: in ‘design/applied’ sciences the identified skills outnumber the identified knowledge elements. Even though some theoretical or even epistemological elements about engineering and technology appeared in the study, the main emphasis still seems to be given to ‘the ability to do’ (Keevy & Chakroun, 2015).

Fig. 1
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Disciplinary Elements Overview

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On the contrary, the opposite occurs regarding science, which traditionally belongs to ‘natural’ sciences (Nathan et al., 2013). It seems that participants mentioned comparatively much more knowledge elements than skills regarding science. Noteworthily, many teachers mentioned inquiry skills in their lesson plan descriptions or in the question related to teaching strategies; however, they did not explicitly include that in this question regarding scientific knowledge and skills. Therefore, explicit identification of scientific skills e.g. inquiry skills seemed limited.

On the other hand, concerning mathematics, we could say that the fact that skills outnumber knowledge is something we wouldn’t actually expect since mathematics is − at least stereotypically − considered a theoretical science. However, as it seems from the sample of participants, teachers tended to identify mathematics under a STEM approach more in the light of skills and applications of mathematics, such as using graphs, statistical analysis, using ICT tools for organising and elaborating data, etc. One could claim that this rather reflects the ‘instrumental’ use of mathematics in STEM, as it is been discussed in the literature (Tzanakis & Thomaidis, 2000) and also becomes apparent in the reflection of a science teacher below:

Rarely a science teacher will pay attention to the deep meaning of mathematics. That means that we, as science teachers, use mathematics but we do not go further than that (AS1, reflection).

Even though an adequate variety of mathematical concepts/knowledge was mentioned by teachers in this study, the practical or maybe even the ‘instrumental’ use of mathematics still seems to be there. We can see that the extensive use of mathematics for graphs and statistical analysis is what gave more emphasis to mathematical skills rather than theoretical mathematical knowledge.

Figure 2 shows the average disciplinary elements that teachers stated in their lesson plans in relation to their own disciplinary background. A pattern that appears in this part of the analysis is that participants tended to identify disciplinary elements from their own discipline to a greater extent, as happens in science, technology and mathematics teachers. Furthermore, many teachers also added that the orientation of their teaching would still give focus to their own discipline.

Now, obviously, the lesson plan varies according to the person who presents it. Because, obviously, that will be implemented by one person, s/he will give an additional emphasis, without being necessary, I think that it will turn like this because of her/his discipline. If s/he dedicates X amount of time in the, for example me that I am a physicist dedicate X amount of time in the construction of the greenhouse, I will dedicate 3X amount of time in data collection or how do these data affect the project. Also, I will dedicate X amount of teaching time for transferring data to the online platform. (AS1, A7 LC)

Fig. 2
figure 2

Mean Values of Knowledge and Skills Disciplinary Elements Identified per Teacher in Relation to the Disciplinary Identity of Teachers. On the x-axis, the first letter represents the discipline and the second letter whether it is knowledge or skills, e.g. SK means scientific knowledge and SS scientific skills

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Therefore, these results concerning elements of their own discipline could be interpreted not only from the expected familiarisation with their own disciplinary ‘home’, but also from the unequal orientation that some teachers had across disciplines in their STEM lesson plans. On the other hand, that did not seem to be the case with engineering teachers who had comparatively low mean values on identifying elements in their own field.

Interdisciplinary Analysis: Interconnections among Disciplines

In Fig. 3 we can see a visual representation of the distribution of identified elements in relation to the disciplinary background of teachers. It is notable to state here that, in some cases, in the same concept/phenomenon/application teachers identified some additional disciplines that others did not. For example, in teaching about batteries (operation, types) of the artefact, some teachers identified common ground between science and technology, while one teacher also added that mathematics are also involved when studying curves of charging/discharging, and another teacher mentioned that all STEM disciplines are actually involved in it. Hence, a teacher could see a different set of disciplines when approaching the same interdisciplinary element.

Fig. 3
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Interconnections per Disciplinary Background

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Furthermore, in an effort to identify patterns between the interconnected disciplines mentioned and the disciplinary background of the teachers, we will examine once more the mean values of interconnections per teacher. In specific, we will try to inspect to what extent a teacher tends to identify interconnections between his/her own discipline in contrast to interconnections between disciplines that do not involve his/her own discipline. Therefore in Fig. 4, we can see the mean values of interdisciplinary elements that involve a discipline (e.g. Science) in contrast to elements that do not involve this discipline (e.g. NonScience).

Fig. 4
figure 4

Mean Values of Identified Interconnections per Individual Teacher & Disciplinary Background

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As we can see in Fig. 4, science teachers of this study tended to identify interconnections involving science to a greater extent in comparison to interconnections without science. This is also the case with technology and mathematics teachers. In a general sense, it seems that teachers tended to trace more interdisciplinary elements involving their own discipline, a result which seems to be in accordance with the results from the disciplinary analysis in the previous section.

However, this is not the case with interdisciplinary elements related to engineering. Most teachers had greater mean values on elements that do not involve engineering in contrast to the ones that include engineering. Even engineering teachers had similar levels in both categories (with & without engineering). We could hypothesise that this relates to the vagueness on the understanding of what is engineering at the K-12 level, as appeared in the previous section. Also, the fact that the artefact development was made partly and exchanged in turns among individual teachers due to cοvid restrictions could have also impacted this result.

Another pattern that needs attention is the inclusion of mathematics in the identified interdisciplinary elements. Despite mathematics teachers who tended to include mathematics in the interdisciplinary elements mentioned, the rest of the participants generally tended not to. This tendency could be interpreted in terms of the marginalised role of mathematics in STEM, as stated in the literature. On the other hand, interdisciplinary elements highvalued technology, as well as science. This result is also reflected in the collaboration trends that teachers mentioned in their reflections, as it has also been analysed by Nipyrakis et al. (2024).

Interdisciplinary Analysis: Boundary Objects

The second part of the interdisciplinary analysis relates to the identification of concepts/phenomena/applications that could not be effectively taught under a unidisciplinary approach. Therefore, these themes ‘exist’ in multiple disciplines, apart from their own nature; in other words what we shall codify as boundary objects.

In specific, in Fig. 5 we can see the distribution of the codified responses of the teachers in the lesson plan question, which were paraphrased and codified in the 4 categories that the IDENTITIES project (www.identitiesproject.eu) suggested: concepts/phenomena, methods/techniques, artefacts/objects and questions/justifications.

Fig. 5
figure 5

Boundary Objects Coded per Disciplinary Background of the Teachers

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Some main patterns that appear in each discipline of the teachers of this case study are as follows: as regards science teachers, they highlighted the conceptual nature of boundary objects, (e.g. photosynthesis, self-assembly of DNA) as well as the materialistic one i.e. the identification of objects or constructed artefacts (e.g. photovoltaics, aeroplane motors). Contrastingly, technology and engineering teachers emphasised the methods/techniques dimension (e.g. calibration, programming). Finally, mathematics teachers’ perceptions were quite distributed, although the conceptual nature prevails.

The findings show that the epistemological background still played a role, as occurred in previous parts of the analyses. We can see discrimination between the natural sciences and the design sciences in the present study, since the latter emphasised the methods and techniques, while the former tended to use more conceptual themes as a vehicle to foster interdisciplinary teaching. In other words, teachers with a natural sciences background preferred theoretical constructs in order to approach and teach STEM integration, while the ones with a design sciences background preferred processes. However, notable is the fact that science teachers also valued artefacts/objects. We could interpret this result in light of the previous analysis concerning the key characteristics found in the lesson plans. Many science and mathematics teachers used the artefact(s), but many of them used it just for demonstration or for data collection purposes, and not for designing and constructing it, which puts the focus on the process. On the contrary, design science teachers tended to follow a different pattern by making more use of the artefact development phase.

Discussion

In this study we analysed the STEM lesson plans that in-service teachers coming from S-T-E-M backgrounds designed. Teachers’ lesson plans, both from their deliverables and from their oral descriptions during the LC meetings were analysed in terms of a) the content of the lesson plan in relation to the STEM key characteristics they implemented and the sequence of the activities they followed, and b) the disciplinary and interdisciplinary elements that teachers identified in them.

Disciplines and Interdisciplinarity

One of the main findings of this study is that divergencies take place at the disciplinary level when teachers design STEM teaching at many different levels. First, the participants identified more disciplinary as well as interdisciplinary themes that were related to their own disciplinary backgrounds. One could argue that this finding was to be expected given that teachers have increased familiarisation and depth in knowledge and skills regarding their own disciplinary roots. Hence, that is something that could be expected since they have expertise in this discipline. However, qualitative analysis reveals that divergence also occurred in relation to teachers’ orientation, since teachers would even admit to intentionally drawing unequal attention to disciplines, often prioritising their own.

A second major finding is that teachers coming from different disciplines had different positioning regarding some integrated STEM key characteristics. Specifically, it was common that teachers coming from ‘natural’ sciences incorporated the contextualisation with the real-world problem in a more explicit and integral way than their ‘design’ sciences peers, a divergence which aligns with the theoretical underpinnings described in Quinn et al.’s (2020) model. On the contrary, many natural sciences teachers engaged very peripherally with engineering design, e.g. many of them just demonstrated the artefact or explained about it, while many of their design sciences peers exclusively built their teaching about or ‘around’ the artefact (e.g. constructing, coding). In this light, King and English (2016) stated that focusing on the construction of the artefact may well overshadow the core science and mathematics concepts. This issue creates a discussion about STEM design practices and whether and how the artefact construction, the real-world problem and the natural sciences content could be in balance, or at least not marginalise any of the three.

Third, a boundary design practice was also noted in the descriptions of the STEM lesson(s): the sequence of the activities that teachers developed. Some design sciences teachers set the development of the artefact as the backbone; science content could follow, or just frame the artefact development. Contrastingly, most participants, especially the natural sciences ones, preferred to mention or use the artefact after the theoretical instruction, a pattern which also appeared with many elementary teachers (Pleasants et al., 2021). On the other ‘extreme’ perspective, some science teachers assimilated clearly their disciplinary practices, i.e. some science teachers conceptualised STEM as an experimental setting. These differences in the type and the row of the activities reveal diverse paths in designing STEM among teachers.

Fourth, the nature of the boundary objects that teachers identified in order to teach integrated STEM also differed based on their discipline. Natural sciences teachers tended to prefer conceptual entities while design science teachers mostly emphasised the process/methods. Hence, although reflection on boundary objects facilitated the discussion about interdisciplinarity, each disciplinary ‘tribe’ used different tools to approach or introduce interdisciplinary thinking to students.

Concluding, we can infer that disciplinary backgrounds affect not only the disciplinary and interdisciplinary themes that teachers include in their designed STEM lesson plans, but also the key STEM characteristics they put emphasis on, the sequence of activities as well as the nature of the boundary objects they use for teaching integrated STEM. However, it is important to note here that the above results refer to general tendencies across disciplinary groups, while a considerable number of teachers did attempt to cross boundaries and initiate things out of their ‘comfort zone’.

Nature of the S-T-E-M Disciplines

It is noteworthy to add here some reflections about the disciplines, as they were recognised by teachers. The findings of this study reveal some characteristic − or even stereotypical − nuances about the disciplines. In specific, teachers mostly identified elements of science in terms of knowledge while in the cases of technology and engineering mostly in terms of skills. On the one hand, this perspective seems reasonable in light of the stereotypical ‘natural & design’ categories that exist in the literature (Nathan et al., 2013). One could claim that these results make sense since teachers are called upon to integrate knowledge and skills from different disciplines that they often do not have sufficient understanding of. Consequently, this synthesis would tend to make use of disciplines in a rather stereotypical way, i.e. using science as content, mathematics as an instrument for analysis, and application skills from the design sciences. Besides, these generic differentiations are elements that assist teachers to understand the boundaries among disciplines.

Furthermore, as regards engineering, the findings reveal that there is a lack of clear understanding of what is engineering in educational contexts among teachers, even among teachers who have an engineering background. This paradoxical result could be attributed to three factors. First, there is quite an extensive affinity between engineering and technology at the epistemological level (Murphy et al., 2015), and quite often, the boundaries between these two disciplines are vague. For example, in the present study one teacher mentioned ‘design’ in the technology domain, although it is rather considered a characteristic of engineering and the central difference between the two disciplines (Murphy et al., 2015). Second, there seems to be limited or even a lack of understanding of what could be considered engineering at the K-12 level. Although NRC (2014) definition was initially presented to teachers, teachers still asked the LC group for clarifications on what we define as engineering, as appears in transcripts. Indicative is also the fact that this discipline-related question was the only one left blank by one engineering teacher in his lesson plan. Third, it is quite common in the Greek context to use the word ‘μηχανική’ as a rather misleading translation of the term ‘engineering’, since the same word is used for mechanics, the chapter of physics. Particularly, in the lesson plans of two teachers, 3 codes (e.g. motion) were inaccurately identified in the engineering domain. Therefore, this terminology problem seems to enforce the problem of identifying engineering knowledge and skills. Overall, it seems that there is a need for more explicit instruction on engineering education for teachers.

Contributions & Implications

The present study provides empirical contributions towards the theoretical integrated STEM framework in terms of its relevance and applicability to practice. Specifically, we can see the ways that each key characteristic is been implemented in the design of STEM teaching as well as the extent to which it is been implemented. In this light, findings can inform teachers’ affordances and challenges towards implementing specific STEM characteristics. One notable case is promoting STEM careers, which was the characteristic that was least implemented by teachers, although it is stressed in STEM frameworks (Roehrig et al., 2021). Hence, more support is needed in order to highlight this dimension.

Limitations of the study relate to the small number of participants per discipline; therefore personal preferences and interest might have influenced the findings. Also, the fact that participants voluntarily participated in the study does not make them a representative sample, since they already had increased motivation in STEM. Furthermore, the fact that most sessions took place online may have affected the engineering process of developing the artefact, which inevitably has affected teachers’ lesson plans regarding this part, especially the ones who had no experience with it. Moreover, teachers’ lesson plans and identified interdisciplinary elements and boundary objects relate to their own lesson design choices and STEM views; hence they may deviate from the teachers’ instructional practices in the classroom.

Overall, the findings of this case study have the potential to inform the existing knowledge base on STEM education and the design of PD programmes. Particularly, implications for practice relate to the identification of existing disciplinary peculiarities and boundary STEM design practices. Hence, individualised assistance and instruction based on teachers’ disciplinary backgrounds and orientations are recommended when designing PD in order to overcome specific boundary obstacles. Moreover, it is recommended that PD programmes promote cross-disciplinary collaborations to make use of teachers’ specific knowledge and expertise that differ from peers. Regarding implications for research, the study proposes the use of interdisciplinary means such as boundary objects in order to assist the design of interdisciplinary instruction. In addition, the study sheds light on the extent and the way that teachers include STEM key characteristics in their instructional design practices. Future research, for example, could further explore the ways in which teachers implement STEM key characteristics in their instructional practices and how the use of boundary objects facilitates student understanding.

Prospected results from such PD approaches would be to enrich teachers’ ability to design and implement integrated STEM, by incorporating key STEM characteristics that they often neglect or address difficulty with, in order to provide more cross-boundary and holistic STEM experiences to students, and a higher degree of meaningful integration among disciplines.