Some studies have shown that pupils from single-sex schools outperform their counterparts at mixed-gender schools.
This column attempts to disentangle the causal effects by exploiting a government policy in South Korea that led to some single-sex schools converting to co-ed one grade at a time. Academic performance fell for boys when their schools became co-ed even if their class remained single-sex, but performance only fell among girls whose classes became mixed. These results suggest different mechanisms for the effects of mixed-gender schools on boys’ and girls’ academic performance.
In recent years, single-sex education has attracted much policy interest as a potential tool for promoting pupils’ academic achievements and closing various types of gender gap. Proponents of single-sex education argue that the single-sex environment is beneficial to academic achievements for reasons such as students avoiding the attraction of the opposite sex, and being less likely to suffer from gender stereotypes. On the other hand, advocates of mixed education argue that boys in co-ed schools perform better as they are surrounded by female peers who are better behaved, and who perform better academically. Moreover, for both boys and girls, the mixed-gender environment is argued to be more conducive to the development of social skills, better preparing them for the ‘real world.’
A key question, therefore, is whether or not a single-sex environment improves pupils’ achievements and whether the effects are common for both genders. To make progress on this, one needs to estimate the causal effect of pupils’ exposure to single-sex versus mixed-gender peers. Estimating this effect is challenging, most importantly because the endogenous processes that sort students into schools.
Research questions and design
We address this very question in a recent paper (Dustmann et al. 2017). We build on Park et al. (2013) who use an assignment policy in Seoul, South Korea, where students were randomly allocated to academic high schools within districts. These authors show, using data for a single cross-section (for the year 1999), that boys (girls) who were randomly assigned to all-boys (all-girls) schools outperform their counterparts at co-ed schools. However, the existing single-sex and co-ed schools in Seoul may differ not just in their pupil gender type but also in various observable and unobservable inputs that can affect student achievement. Therefore, even if pupils are randomly allocated to a single-sex versus a co-ed school, any differences in pupils’ outcomes between schools could be due to pupil gender type (the direct effect of pupil gender composition), or other observable and unobservable differences in school inputs (school effects). In turn, the direct effect of pupil gender composition could be due to exposure to mixed-gender peers at the school level, or at the classroomlevel. For policymakers who are considering creating a new single-sex school or a single-sex classroom, the key question is whether there are any direct benefits to being exposed to a single-sex versus mixed-gender learning environment on either the school or classroom level.
Total effect of single-sex versus co-ed schools
We identify three distinct parameters, using administrative data on the national college entrance exam, taken by South Korean 12th graders in 1996-2009. To address the sorting problem, we use – similar to Park et al. (2013), though based on multiple years of data – the random assignment of pupils to schools within school districts at each cohort. This allows us to address our first question: