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While enrolment rates disaggregated by sex might be easy to find, comparative cross-country data on how many children are in single-sex schools are scarce. As another International Women’s Day passes us by, it seems fitting to also ask the question whether single-sex schools are beneficial or not; evidence on this front is mixed as well. What do we know?

One place to look is cross-national learning assessments, such as the Programme for International Student Assessment and the Trends in International Mathematics and Science Study (TIMSS). In about 60% of education systems in the mostly upper-middle and high-income countries that took part in the 2015 TIMSS, less than 5% of primary schools were single-sex.

However, as the graph above shows, gender segregation in separate classes or schools is common in countries as diverse as Chile, Ireland, Israel and Singapore and is prevalent in many Muslim-majority countries. The prevalence of single-sex schools also generally increases in secondary education, for instance from close to zero for primary to almost one in five for lower secondary education in England (United Kingdom).

In most countries, the proportion of students in single-sex schools corresponds to the proportion of such schools. Exceptions relate to the size and type of schools that tend to be single-sex. In the Islamic Republic of Iran, for instance, single-sex primary schools (66%) enrol 84% of grade 4 students, partly because public single-sex schools are larger than private co-education schools. By contrast, single-sex primary schools in the Russian Federation (8%) account for only 1% of grade 4 enrolment, as single-sex religious and/or private schools are smaller, on average.

We can also capture some information about changes over time from the countries that participated in both the 2007 and 2015 TIMMS. We find that single-sex schooling decreased in Australia and the Republic of Korea. The latter shifted to co-education schools in the 1980s, and a recent policy decisively favours co-education.

The situation is more complex in Western Asia, however. In Jordan, the share of single-sex lower secondary schools increased by 8 percentage points and the share of students attending them by 12 points. One reason may be the influx after 2011 of Syrian refugees, who attended public single-sex schools. The share of single-sex schools meanwhile decreased in Bahrain and Kuwait. While public schools remain segregated in Gulf Cooperation Council countries, the changes are attributable to an increasing share of mixed private international school.  \The United Arab Emirates introduced co-education primary schooling in 2018.

Are single-sex schools advised?

From a gender inclusion perspective, single-sex schooling may be an acceptable temporary compromise when the de facto alternative in some culture- or country-specific contexts is females not attending school at all. Parents may prefer to send daughters to single-sex schools once they reach adolescence; the fact that such schools do not exist in parts of Pakistan is one reason reported for low female enrolment for instance.

Some argue that gender social dynamics are educationally counterproductive. Females may show greater affinity for and achievement in science, technology, engineering and mathematics when less exposed to negative gender stereotypes about ability and to males monopolizing equipment. Yet single-sex schooling is unlikely to affect choices, attainment or achievement unless it challenges dominant notions of masculinity and femininity. The counterargument is that single-sex schooling might be alien to reality, and may prevent females from developing social skills needed to navigate unsegregated workplaces and adult life.

Evidence on the effects of single-sex schooling, meanwhile, is mixed. The main difficulty is isolating the characteristics of students likely to attend single-sex schools and those of segregated schools so that evidence is not biased. In Thailand and Trinidad and Tobago, single-sex schools tend to attract wealthier females, for instance, leading to overestimation of the benefits. A meta-analysis of 184 studies from 21 countries found that, while some showed modest learning outcome benefits of gender segregation, higher-quality research that adjusted for confounding factors showed little to no benefit and a slight negative effect on female education aspirations. The Republic of Korea provides one of the few natural experiments, as students are randomly assigned to secondary schools. A study exploring this particular case found that single-sex schooling had a small positive effect on achievement.

Malta presents an interesting case of a country that has moved from predominantly single-sex secondary school to co-education. State-run primary schools there have been co-educational since 1980, while secondary schools were single sex until 2013. Due to this history and the many single-sex church-run schools, the prevalence of single-sex secondary schools is among the highest for non-Muslim-majority countries. A study on the centralized lottery for Catholic school admission suggested that students with single-sex schooling subsequently chose less gendered subjects. Malta’s recent move towards public co-education occurred as part of a framework of policies to support and promote social inclusion. One benefit is easier inclusion and freedom of expression of lesbian, gay, bisexual, transgender and intersex students, who may be particularly excluded in single-sex schools premised on a homogeneous gender identity. With its 2015 Gender Identity, Gender Expression and Sex Characteristics Act, Malta adopted Europe’s first comprehensive education policy focused on their needs; it included confidentiality and ended gender segregation in uniforms and some sports.

Single-sex schools may reflect parental choice – a type of self-segregation, which is a challenge to the purest sense of inclusion in education. But there are many reasons why parents might choose single-sex over co-educational schools for their children, as the Pakistan example above attests. This is why the 1960 UNESCO Convention against Discrimination in Education accepted that, under certain conditions, single-sex schools did not constitute discrimination. The question, then, perhaps should not be which setting is better but why single-sex schools sometimes produce better outcomes and how to replicate those benefits in more inclusive settings.