Girls’ schools consistently top the league tables at GCSE and A level — which the author suggests is attributable to selection and background, rather than gender.

Advocates of single-sex schooling argue that children achieve more academically when they are taught separately. After reviewing a decade of international and national research, Alan Smithers, director of the Centre for Education and Employment Research at the University of Buckingham, says that the evidence does not support this view.

“On performance, there is no evidence that girls will get better results in a single sex than a co-educational school. The same is true for boys,” Professor Smithers said. “The girls’ schools feature highly in the league tables because they are highly selective, their children come from particular social backgrounds and they have excellent teachers.”

The number of single-sex state schools has declined from 2,500 in the 1960s to 400 today. In the independent sector, 130 single-sex schools for boys and girls have merged, turned co-educational or closed. Many single-sex comprehensives perform relatively poorly overall.

“If you look at GCSEs and at A-level results, girls overall do better than boys,” Professor Smithers said. So, on average, a girls’ school would achieve better results than a boys’ school. “However, if you have a highly selective boys’ school, they will do better than most girls,” said Professor Smithers, who this week presents his findings at Wellington College, which recently turned co- educational.

Last year 23.9 per cent of girls were awarded A grades at A level, compared with 21.5 per cent of boys. In most subjects, with the exception of English and modern languages, girls outperformed boys.

Professor Smithers, who sent both his daughters to a single-sex school, is keen not to diminish the schools’ achievements but insists that their emphasis on gender is misplaced.

He cites, for example, the claim that girls in single-sex schools are more likely to study science than if they study alongside boys. According to his research, this is simply not the case. The proportion of girls taking physics went up between 1960 and 1985 — at a time that single-sex schools in Britain were disappearing. The trend, he says, appears to have been caused by the new mixed comprehensives offering girls more opportunities to take physics.

“The pattern emerging was that girls were at least as likely or more to study physics in co-ed schools, possibly because of the critical mass of students, the facilities and the teachers,” said Professor Smithers. This was particularly the case among the brightest girls.

His research will be unwelcome to the top boys-only public schools such as Eton, Harrow and Radley — as well as to the country’s 203 feepaying girls’ schools.

They point out that last year girls and boys in single-sex independent schools achieved 10 per cent more A grades at A level than those at independent co-educational schools.

Brenda Despontin, president of the Girls’ Schools Association and head of Haberdashers’ Monmouth School for Girls, says that single-sex schooling offers more than academic achievement. “Children have the opportunity to develop at their own pace, to grow in confidence and not worry about others around them,” she said. “They gain much more than As at A level — they come out aiming high and confident of taking the world by storm.”

Last year a study by academics at Cambridge University suggested that single-sex classes within co-educational schools could be the key to helping adolescent boys and girls succeed. Schools that taught boys and girls certain subjects separately — to address differentials in achievement — found that both became more confident and grades climbed rapidly.

This “parallel education” is favoured by Steve Biddulph, the Australian educational psychologist and author of Raising Boys. After 20 years of research he believed that there was strong evidence to suggest that boys and girls aged between 12 to 15 did not learn well together.

“The reasons are developmental — there is an almost two-year difference in the onset of puberty, so girls leap ahead physically and emotionally,” Mr Biddulph said.

Among his suggestions were that although boys and girls should mix in the playground, in their teens they should learn separately until they reached the age of 16.

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