A report which claims that girls do not suffer academically by going to co-educational schools, despite the achievements of single sex schools in the exam league tables, has failed to convince the girls’ school movement.

The report, Co-educational and Single Sex Schooling, by Professor Alan Smithers and Dr Pamela Robinson of Manchester University’s Centre for Education and Employment Research, examines the results and intake of schools at the top of exam league tables.

It concludes that they do well because they are highly selective and draw pupils from families of high social classes. Girls’ schools also do well, particularly at GCSE, because girls’ results are generally better than boys’.

Over time these schools, like top football teams, have been able to build on their reputation and attract talent from far and wide, say the authors.

The report, commissioned by the co-educational group of the Headmasters’ Conference, comes ahead of the publication of A-level league tables for the independent sector on Saturday.

Of the 240 HMC schools, 135 are fully co-ed and a further 30 accept girls into the sixth form. In the last decade the number of schools to become co-educational has more than doubled.

It has been almost exclusively boys’ schools which have made the switch, largely out of parental pressure and economic advantage or necessity.

In the maintained sector only a handful of single sex, generally grammar schools, have survived. In 1961 there were 1,400 girls’ and 1,400 boys’ schools.

However, the exam league tables have shown that single sex schools, and disproportionately girls’ schools, get the best results.

The report discloses that at A-level, half of the top 48 independent schools were girls’ schools compared with the 40 per cent that might have been expected. Of the top 48 top state schools, a third were girls’ instead of the expected 9 per cent.

This year’s results have shown girls’ schools increasing their high positions.

It appears, however, that seven of the schools with the highest A-level results will be boys’ independent schools.

While the report puts the appropriate spin on the statistics to support the HMC co-educational schools, it notes that there is no information available on the relative performance of girls in girls’ schools and those in co-educational schools.

The authors said the interim report was a challenge to the Girls’ Schools Association, which represents 230 independent schools, to respond. The GSA was accused of “stonewalling” when asked for co-operation.

This was firmly denied by Sheila Cooper, the GSA’s general secretary. She said while she had been consulted in the early stages, the co-ed group had decided to take a different tack and that she had not been involved any further. The HMC also distanced itself from the report.

Kaye Harrison, head of Newport Girls’ High, Shropshire, where all pupils taking GCSE last year obtained grade A to C in at least eight subjects, said: “We get good results because we are selective, but I do believe girls can benefit from being taught without boys. They are allowed to develop at their own pace and in this school they are taught to believe they can do anything.

“Girls’ schools also provide strong role models. When I was teaching maths at a mixed comprehensive, more girls chose to study it further than in classes taken by men teachers.”