Mean and distributional impact of single-sex high schools on students’ cognitive achievement, major choice, and test-taking behavior: Evidence from a random assignment policy in Seoul, Korea

•The mean effect of single-sex education is small when self-selection is accounted for.•The effect is larger for the average-performing students.•The effect is trivial for students located at the very bottom and very top quantiles.•Single-sex schooling has few impact on major choice and test-taking behavior.

Single-sex schooling has been considered in many countries as a way to promote student achievement. This paper estimates the mean and distributional impact of single-sex high schools on students’ cognitive achievement, major choice, and test-taking behavior—by exploiting the random assignment policy adopted in Seoul, Korea. Based on administrative data for a period of seven years, I find that, on average, the positive effects of single-sex schooling on test scores are small, especially when the parental and teacher sorting are accounted for. Although the magnitude of the estimated effects is small, I find that the effect is relatively larger for students in quantiles 0.5–0.8 of the distribution of test scores. The impact is trivial, on the other hand, for students located at the very bottom and the very top quantiles. Moreover, I do not find any differences, both practically and statistically, in major choice and test-taking behavior.