The study, by Peter Daly of Queen's university, Belfast, and Neil Defty of Durham university, will disappoint supporters of single-sex schooling who say both girls' and boys' schools boost achievement and provide diversity and parental choice in the state sector.
To complicate the issue further, a small study in the United States suggests that boys and girls can benefit from being taught separately - but they have to be in the same school.
Children in single-sex classes in co-ed schools do better than those in mixed classes, it found. The research also found that 11 to 14-year-olds focused better in boys or girls-only classes, and younger pupils were most likely to benefit, said author Frances Spielhagen, a research fellow at the American Educational Research Association.
Shenfield school in Brentwood, Essex, is a mixed school that teaches all its 11 to 14-year-olds in single-sex lessons. The older pupils are separated for the core subjects. Beverley Swan, assistant head, said:
"Children like it. They are able to concentrate better in single-sex classes, but if you look at our playground it is like any other. Teachers can tailor what happens in the classroom much more carefully."
Last November, David Miliband, then schools minister, surprised the education world when he backed segregated classes. The evidence in favour of single-sex classes in mixed schools was startling, he told the Girls'
Schools Association annual conference.
Supporters of single-sex teaching argue that segregation boosts pupils'
confidence, encourages them to participate more in lessons and reduces the incentive to show off.
The study by Dr Daly and Mr Defty is based on maths performance and attitude of 42,000 pupils in 294 schools that took part in Durham university's Yellis project, which analyses the progress of 14 to 16-year-olds. They found that girls attending single-sex schools had a better attitude to maths than their peers in mixed schools. But boys in single-sex schools did not.
FRIDAY MAGAZINE 11 Differential school effectiveness: single sex schooling revisited by Peter Daly and Neil Defty is available from email@example.comSeparate by choice: Single-gender academic classes in a public middle school is available from firstname.lastname@example.org