Does single-sex schooling improve academic performance?

Do students in single-sex schools or classrooms achieve better academic outcomes (test scores, grades, course-taking, graduation, college entry) than comparable students in coeducational settings, once selection into single-sex schooling is accounted for, and does the answer differ for girls and boys?

Probably not

Summary:

The raw test-score advantage of single-sex schools is real but driven by which families choose them — private governance, religious management, and academic selectivity explain most or all of it. No credible study finds a meaningful benefit from gender separation itself, for either sex, once these factors are removed. The evidence base is narrow (Seoul, Trinidad and Tobago, 1970s Britain) and may not generalize to the settings where this debate is loudest.

The parts of the question

The short answer

Students at single-sex schools score slightly higher on exams in raw comparisons, but this advantage shrinks or disappears in every study that accounts for school type — private versus public, religiously governed versus secular, academically selective versus open. The largest meta-analysis, pooling 184 studies and 1.6 million students across 21 countries, found controlled effects near zero for both sexes in math, science, and reading (Pahlke 2014). Studies without selection controls show modest advantages; studies with controls do not. The performance gap is real, but it traces to the institutions, not to the absence of the other sex.

Where the belief comes from

Single-sex schools are disproportionately private, religiously managed, or academically selective. In Seoul, where a government lottery assigns students to schools, 80 percent of single-sex schools are private compared with 30 percent of coeducational schools (Park 2012). In Trinidad and Tobago, 91 percent of single-sex schools are run by religious bodies (Jackson 2012). Families who choose these schools tend to be wealthier, more educated, and more invested in academics. When studies compare single-sex students to the general coeducational population without adjusting for these differences, the single-sex students look better — but the comparison is between a curated group and everyone else. Lee 1986 claimed girls especially benefited from single-sex Catholic high schools, but 87 percent of the girls' schools were run by religious orders versus 8 percent of the coeducational comparison schools — a difference the paper acknowledged it could not separate from the single-sex effect.

What is established

The apparent advantage is a selection artifact. Pahlke 2014 found that studies controlling for student background produced differences close to zero, while uncontrolled studies consistently showed larger advantages. In Seoul's lottery system, girls' small advantage (roughly moving from the 50th to the 52nd percentile) vanished once Dustmann 2018 controlled for teacher gender ratios and private-school status. In Trinidad and Tobago, Jackson 2012 found that the apparent advantage shrank by roughly two-thirds after removing selection bias.

For boys, the null is settled. No credible study finds boys doing better in single-sex settings after accounting for selection. Park 2012's boys' college-attendance advantage dropped 57 percent with a single control for private-school status, and the authors noted — without publishing the data — that controlling for teacher gender composition "substantially reduced" the remaining effect.

For girls, the picture is similar but with one caveat. Sullivan 2010, following a British national birth cohort, found that girls at single-sex schools had roughly twice the odds of reaching the top exam benchmark at age 16, after controlling for family background and prior scores. But this advantage did not persist to age 18 exams, university degrees by age 33, or adult skills. One durable pattern did appear: girls at single-sex schools were more likely to succeed in science and math, extending into the fields they qualified in by age 33. Whether this reflects the school environment or unmeasured family characteristics — parents with less traditional gender attitudes choosing single-sex schools — cannot be determined from the data.

What is not established

That gender separation itself causes any academic benefit. Every positive result in this evidence base is confounded with institutional differences. Park 2012 claimed Seoul's lottery proved a causal effect but never separated single-sex classrooms from private governance. Lee 1986's Catholic-school finding is confounded with religious-order management. Jackson 2012's small positive result for the 15 percent of girls who strongly preferred single-sex schools could not be separated from the specific religious all-girls schools those students attended.

That single-sex schooling harms performance through increased stereotyping. Halpern 2011 argued this, but no cited study measured stereotyping in students who actually attended single-sex schools — the evidence came from laboratory experiments on children sorted by t-shirt color.

That minority boys benefit from single-sex programs. Pahlke 2014 flagged this as the subgroup where advocacy is strongest and evidence thinnest — too few well-designed studies exist to evaluate the claim.

How old is the evidence

The strongest studies rely on data a decade to half a century old. Sullivan 2010's cohort entered school in 1969. The Seoul data run through 2009. No study in this evidence base uses data from the past decade. The recent expansion of single-sex programs in U.S. charter schools is unrepresented.

Limitations of this evidence base

The evidence comes almost entirely from three settings — Seoul, Trinidad and Tobago, and 1970s Britain — each with an educational system unlike the ones where single-sex schooling is debated today. Seoul assigns students by lottery to a uniform national curriculum. Trinidad and Tobago uses a centralized algorithm. Britain in the 1970s had strict catchment-area rules. None resemble the U.S. or contemporary U.K., where single-sex schooling is a choice made by specific families in a market of options.

Missing entirely: large-scale evidence from U.S. or U.K. public schools with credible causal designs, studies of single-sex classrooms within coeducational schools (the format most U.S. programs actually use), evidence on ethnic minority students, and any study reporting the educational philosophy of the single-sex program — 92 percent of studies in Pahlke 2014 did not.

What is still open

Whether single-sex classrooms within coeducational schools help. The one study that isolated this (Dustmann 2018) found a signal in girls' language scores, but it rested on just four converting schools — too few to draw conclusions.
Whether specific subgroups benefit. Minority boys in U.S. cities are the population most targeted by single-sex programs and least represented in the evidence.
What happens in the classroom. No study in this base measures teacher behavior, peer dynamics, or stereotype threat in single-sex versus coeducational rooms. Without a mechanism, even a positive result would be hard to act on.
Whether the science-and-math pathway for girls is real. Sullivan 2010's finding that girls at single-sex schools were more likely to pursue science persisted into their thirties, but the observational design cannot rule out family selection. Randomizing girls into single-sex science classes could test it directly.

The papers behind it

Every paper this answer rests on, with the verdict from its Litmus review. The answer gives weight only to claims those reviews found supported.

Where the claim comes from

Effects of single-sex secondary schools on student achievement and attitudes.Lee and Bryk (1986). Journal of Educational PsychologyDubious — probably doesn't hold up
Claims that single-sex Catholic high schools produce better academic outcomes than coeducational ones, especially for girls. The strongest findings are for girls' schools, but 87% of those schools were run by religious orders versus 8% of coeducational schools — a confound the paper itself calls inseparable — so the results cannot distinguish gender separation from a different style of institutional management.

Original studies

Single-Sex Schooling and Academic Attainment at School and Through the LifecourseSullivan et al. (2010). American Educational Research JournalCredible — likely right, with caveats
Using a British birth cohort from 1958, this paper finds that girls at single-sex schools scored higher on national exams at age 16, and that both sexes pursued more gender-atypical subjects (girls in science, boys in languages) at single-sex schools — a pattern that persisted into their thirties. The associations are well-measured and the controls are strong for an observational study, but the paper's causal claims — that co-education intensified gendered patterns and that single-sex environments reduced stereotyping — go beyond what the design can establish.
Academic Performance and Single-Sex Schooling: Evidence from a Natural Experiment in SwitzerlandEisenkopf et al. (2011)Dubious — probably doesn't hold up
This study claims that randomly assigning girls to all-female classes at a Swiss high school raised their math grades by about 10% of the usable range, especially with male teachers, and that the effect works through improved self-confidence. The core design idea — within-school assignment eliminating self-selection — is genuinely valuable, but because the only outcome is teacher-assigned grades with no standardized benchmark, the study cannot distinguish whether girls learned more math or were simply graded differently in single-sex classrooms, and the teacher-gender finding is almost certainly an artifact of having only eight math teachers.
Single-sex schools, student achievement, and course selection: Evidence from rule-based student assignments in Trinidad and TobagoJackson (2012). Journal of Public EconomicsCredible — likely right, with caveats
Uses Trinidad and Tobago's centralized school-assignment algorithm to estimate the causal effect of single-sex schooling — a genuinely clever design that convincingly shows naive comparisons are inflated by selection. The core finding that most students show no benefit is credible, but the more specific claims — that girls with strong preferences benefit enormously, that single-sex schools reduce girls' science-taking, and that universal expansion would be pointless — rest on small subgroups, untested assumptions about course offerings, and extrapolations beyond what the data support.
Causal Effects of Single-Sex Schools on College Entrance Exams and College Attendance: Random Assignment in Seoul High SchoolsPark et al. (2012). DemographyDubious — probably doesn't hold up
Claims that Seoul's lottery-based school assignment proves single-sex schools cause better exam scores and college attendance for both boys and girls. However, 80% of single-sex schools are private while only 30% of coeducational schools are, and the estimated effects shrink 40–57% with even limited controls — meaning the paper cannot separate the effect of gender-segregated classrooms from the effect of private-school governance, teacher hiring, and institutional culture.
Gender, single-sex schooling and maths achievementDoris et al. (2013). Economics of Education ReviewCredible — likely right, with caveats
This paper finds a gender gap in maths favouring boys among Irish nine-year-olds, concentrated at the top of the score distribution, and reports no evidence that single-sex schooling reduces it. The descriptive finding is solid, but the causal claims about single-sex schooling rest on a questionable assumption of random assignment and the study lacks the power to detect modest effects — the headline claim that the gap is actually larger in single-sex schools is not statistically distinguishable from zero.
Why Are Single-Sex Schools Successful?Dustmann et al. (2018). Labour EconomicsCredible — likely right, with caveats
Students randomly assigned to single-sex schools in Seoul scored higher on college entrance exams than those in coed schools, but this advantage disappeared once other school characteristics were controlled for. The paper's most distinctive claim — that mixing boys into girls' classrooms specifically harms girls' language scores — rests on just four converting schools analyzed with statistical methods known to be unreliable at that scale, so the direction of the finding is plausible but the claimed precision should not be taken at face value.

Studies that pool other studies

The effects of single-sex compared with coeducational schooling on students’ performance and attitudes: A meta-analysis.Pahlke et al. (2014). Psychological BulletinCredible — likely right, with caveats
This meta-analysis of 184 studies finds that when studies control for selection effects, the average difference between single-sex and coeducational schooling is small across academic and social outcomes. The directional finding is probably right, but the strong conclusion that single-sex schooling provides 'no benefits' overshoots the evidence — the 'controlled' category mixes strong and weak designs, the 12 truly randomized studies are never analyzed separately, and pooling fundamentally different types of single-sex programs could mask real effects that cancel each other out.

Critiques

The Pseudoscience of Single-Sex SchoolingHalpern et al. (2011). ScienceDubious — probably doesn't hold up
This policy essay argues that single-sex schooling has no proven academic benefits and harms children by increasing gender stereotyping, calling for federal regulations to be rolled back. The argument demands rigorous experimental evidence before accepting that single-sex schools help, but accepts laboratory experiments and preschool correlational data as evidence that they harm — an asymmetry that aligns with all seven authors' roles as founders of an advocacy organization for coeducation, and that undermines the paper's claim to be following the evidence wherever it leads.