Girls at single-sex state schools in England achieved better GCSE results than those in mixed schools, according to analysts.
And all-girls secondary schools slightly outperformed those for boys, an analysis of results in 2015 by education website SchoolDash said.
Some 75% of pupils at single-sex schools achieved five good GCSEs including English and maths, compared with 55% at mixed schools.
It follows comments by a leading headmaster that pupils at all-girls schools could be at a "huge disadvantage" in later life because they had not socialised with boys.
The research looked at results for England's 378 mainstream single-sex state schools, including 161 which are all-boys and 217 all-girls. Around a third are grammar schools.
The analysis showed the advantages for girls-only institutions remained when results were adjusted for other factors including social background and selective intake.
Single-sex school pupils from poorer backgrounds outperformed those at mixed schools, with 61% of disadvantaged students at all-girls schools gaining five good GCSEs compared with 55% in "similar" mixed schools and just 38% across all mixed institutions.
Meanwhile, those with low attainment at primary school made better progress at single-sex schools than their mixed counterparts - 11% compared with 7% - with girls-only students marginally ahead of their boys-only peers.
SchoolDash founder Timo Hannay said: "The overall picture that emerges is one in which single-sex secondary schooling for girls does seem to have some benefits, at least when it comes to these particular measures of GCSE performance.
"Though it's less clear cut, the same may also be true for poor and/or underachieving pupils - ironically the target groups that single-sex schools tend to avoid.
"On the other hand, if you've done all right at primary school, come from a reasonably well-off family, and particularly if you're a boy, then going to a single-sex secondary school is unlikely on its own to improve your grades."
He added: "It also raises the interesting question of why girls (perhaps among other groups) seem to benefit more than boys from single-sex schooling - and what, if anything, the majority of mixed schools might be able to learn from this."
Earlier this month, Richard Cairns, head of Brighton College, said young women could face difficulties if they did not learn to socialise with the opposite sex as children.