Same but Different: Differences in Academic Achievement Between Coed and Single-Sex Classrooms among Coeducational High Schools in South Korea

Students' academic achievement can be influenced by their placement in coeducational or single-sex classrooms, even within coeducational high schools. However, the existing literature has largely overlooked this issue. This study investigates how the gender composition of classrooms in coeducational high schools impacts students' academic performance. To address potential selection bias, we leverage an application-based random assignment system in Gyeonggi Province, Korea. Using an individual-level panel dataset, we find that students in coeducational classrooms exhibit lower academic performance. These results remain robust after controlling for various characteristics, school district fixed effects, and students' school choice preferences. Furthermore, we identify heterogeneous effects by gender, subject, and school year. Finally, we explore potential mechanisms, highlighting school satisfaction and class attitudes as significant channels, particularly for boys.