Despite the voluminous literature on the potentials of single-sex schools, there is no consensus on the effects of single-sex schools because of student selection of school types. We exploit a unique feature of schooling in Seoul—the random assignment of students into single-sex versus coeducational high schools—to assess causal effects of single-sex schools on college entrance exam scores and college attendance. Our validation of the random assignment shows comparable socioeconomic backgrounds and prior academic achievement of students attending single-sex schools and coeducational schools, which increases the credibility of our causal estimates of single-sex school effects. The three-level hierarchical model shows that attending all-boys schools or all-girls schools, rather than coeducational schools, is significantly associated with higher average scores on Korean and English test scores. Applying the school district fixed-effects models, we find that single-sex schools produce a higher percentage of graduates who attended four-year colleges and a lower percentage of graduates who attended two-year junior colleges than do coeducational schools. The positive effects of single-sex schools remain substantial, even after we take into account various school-level variables, such as teacher quality, the student-teacher ratio, the proportion of students receiving lunch support, and whether the schools are public or private.
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In addition to role models, another explanation of the effect of the same-gender teacher is “stereotype threat,” which “refers to a situation where student performance suffers when they fear being viewed through the lens of a negative stereotype threat” (Dee 2007:533) (see also Steel 1997). For example, female students may experience stereotype threat in their math classroom if the teacher is male.
In Korea, middle school students can progress into two types of high schools: academic high schools and vocational high schools. The high school equalization policy is applied only to academic high schools. In recent years, about three of four high school students in Korea have attended academic high schools. In this study, we analyze academic high schools only.
Among 11 school districts in Seoul, one school district, which mainly covers downtown areas with a relatively small number of residents, does not apply the strict random assignment. In this district, students list two to three schools in order of their preference and then are assigned to one of these schools by lottery. We estimate district fixed-effects models, which to some extent should account for this difference. We also tested the robustness of our findings by excluding schools in this particular district, and the results were very robust.
The mean proportion of coeducational schools within districts among 11 school districts in Seoul is .35, with a standard deviation of .48.
The 2008 and 2009 senior cohorts refer to those who were high school seniors in 2008 and 2009, respectively. The academic year in Korea begins in March. The data on college attendance were collected in April 2009 for the 2008 cohort and in April 2010 for the 2009 cohort.
Among a total of 217 academic high schools in Seoul in 2008, we exclude 21 high schools from the analysis. Fourteen of these schools are excluded because they are foreign language, science schools, and other kinds of special schools that are mostly not subject to the high school equalization policy. The remaining 7 schools are excluded because of missing data (no seniors) or other data problems.
Ideally, we would like to include students only in Seoul to make these comparisons on the basis of student-level data comparable to our school-level analysis. However, the number of students only in Seoul is not large enough for reliable estimation. Our analysis with this national-level data set, including Seoul and other equalization policy areas with some modifications, shows that family characteristics and prior achievement of students attending single-sex schools and those coeducational schools are similar. The results suggest that students’ sorting into single-sex or coeducational schools may not be so selective even in the areas of modified randomization. Also note that the KELS survey did not administer academic tests after respondents entered high schools.
Except for the dummy variable for private schools, the four school-level variables are centered on grand means.
The estimates do not change significantly if data from 2008 are also included in these estimates.
In the bottom of the table, the statistics of random effects show residual variances among students within schools, among schools within districts, and among districts, respectively. The results generally indicate that the variability in test scores among schools and among districts is relatively small, consistent with the effect of randomized school assignment aimed to reduce between-school inequality.
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We acknowledge support from the National Academy of Education/Spencer Postdoctoral Fellowship (for Hyunjoon Park), the Spencer Foundation (#20110030), and from the Eunice Kennedy Shriver National Institute of Child Health & Human Development (R03HD066018). The views and opinions expressed herein are those of the authors.
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Park, H., Behrman, J.R. & Choi, J. Causal Effects of Single-Sex Schools on College Entrance Exams and College Attendance: Random Assignment in Seoul High Schools. Demography 50, 447–469 (2013). https://doi.org/10.1007/s13524-012-0157-1
- Single-sex schools
- Random assignment
- Causal inferences
- College entrance
- College entrance exam scores