The amount and type of teacher–student interaction in a Puzzle-based Learning course can vary widely based on the number of students in the course. In our experience, we have taught this course to as many as 300 and as few as 10. Irrespective of the size of the class, it is important that students are active rather than passive. The goal of the teacher should be to get students to use their System 2 thought process as much as possible. Students should treat the course as if it is a workout for their minds, as a mental gymnasium.