We exploit two unusual policy features of academic high schools in Seoul, South Korea—random assignment of pupils to high schools within districts and conversion of some existing single-sex schools to the coeducational (coed) type over time—to identify three distinct causal parameters: the...

We study the effects of random assignment to coeducational and single-sex classes on the academic performance of female high school students. Our estimation results show that single-sex schooling improves the performance of female students in mathematics. This positive effect increases if the...