Inspectors judge girls’ schools to be more successful than either boys’ or mixed, regardless of the social class of the intake, teachers from state girls’ schools learnt last weekend.

Delegates from the Association of Maintained Girls’ Schools also heard that both the ethos and the curriculum of today’s schools are now skewed in favour of “female modes of thought”, particularly at GCSE, and that the gender gap appears very early - a six-month-old baby girl will smile at a human face, but a balloon will serve just as well for a baby boy of the same age.

The only warning note came from Gerard McCrum, an emeritus fellow at Oxford University who traced a link between girls’ poorer performance in finals to the drop in the number of girls’ schools after comprehensivisation in the mid-1970s. He also surprised delegates by revealing that history is the most “gender-sensitive” subject at university - many tutors and examiners still favour stylish polemic (which is, apparently, a male undergraduate trait) over conscientiously balanced argument (the female equivalent).

There are now only about 234 state girls’ schools (including grammar and grant-maintained schools) compared to 2,000 30 years ago, and the number of independent girls’ schools is also diminishing as the fashion for co-education combines with economic pressure in the private sector.

But the more the number of girls’ schools is eroded, the more passionate the defenders of single-sex education seem to become. The issue refuses to go away and the debate is resurrected annually every August when the examination results are published. This year it seems to have gathered momentum in the wake of a report by Alan Smithers, professor of education at Manchester University, which argued that the apparent success of girls’ schools has more to do with their ability to attract the ambitious parents of bright girls than any inherent advantages in separating the sexes.

Delegates were therefore delighted by the evidence presented by Christine Agambar, head of research and analysis at the Office for Standards in Education. The research, which is based on some 5,000 inspections and has not yet been published, compares the performance of girls’, boys’ and mixed schools according to the percentage of pupils eligible for free school meals, the conventional indicator of the socio-economic background of the intake. The results seem to provide strong evidence to refute Professor Smithers’ report.

In the most deprived group (between 40 and 100 per cent of pupils eligible for free school meals) 24 per cent of pupils in girls’ schools obtained five or more GCSEs at grade A to C, compared with 16 per cent in both boys’ and mixed schools. At the other end of the deprivation scale, 91 per cent of pupils from girls’ schools were achieving five A-C grades, compared with 85 per cent in boys’ schools and only 60 per cent in mixed.

Boys’ schools were generally judged more favourably than mixed, though less favourably than girls. Attendance records were similar in boys’ and girls’ schools and both better than mixed, and behaviour, predictably, was much poorer in boys’ schools.

“Girls’ schools are winning across the board,” said Christine Agambar, “we might have to look again at the notion of co-education, if there are such differences across the ability and class range. The data tells me how effective girls’ schools are and also that boys’ schools are more effective than mixed.”

One delegate pointed out that single-sex schools are rare in many of the European countries whose education systems we are often called upon to admire. Ms Agambar said this was due to the effect of “other factors”. OFSTED plans to publish its research on school effectiveness both in the UK and abroad late in 1996 or early 1997. Ms Agambar also said that “the non-white co-efficient has now gone positive” - in other words, the presence of black pupils, whether of Asian or Afro-Caribbean origin, makes a school more likely to be successful.

Earlier, another speaker, Geoff Hannan, provided meat for an anti-feminist backlash, painting a picture of society and education system which overwhelmingly favours females and in doing so could be failing both sexes. Mr Hannan, an education consultant, rattled off a list of supposed intellectual differences between the sexes and then proceeded to show that schools favour the female mind.

At age 11, he said, the average boy is nine months behind in oracy, 12 months in literacy and six months in numeracy.This is because language, the key to intellectual development, is more developed in the female brain and because parents talk to girls more. Girls’ toys may also be more educational because they are more “human”, he added: “The girl talks to her doll or teddy; the boy just makes noises with his car.”

As one delegate commented, “He looks like a charlatan, he talks like a charlatan, but I find myself agreeing with everything he says.”

Mr Hannan also asserted that women are good at “descriptive” and “reflective” thinking but less so at speculation. “At the average dinner party, men and women will describe things, women will then reflect; afterwards men take over with speculation and the women sit back in embarrassment.” Schools, he said, encourage description and reflection at the expense of speculation, thus boring boys and leaving girls understretched.

He also said that girls, were more likely to lack confidence and less inclined to take intellectual risks, and that this could hinder them later at university. “The myth is that boys catch up - they don’t, it’s just that girls’ disadvantage starts showing itself.”

The next speaker seemed to lend weight to this fear as well as providing another argument for girls-only schools. Dr McCrum of Oxford has been analysing A-level and final examination statistics over the past two decades. He says that the number of girls from the state sector getting top grades at A-level (AAA or AAB) dropped dramatically in the mid-1970s, while those from independent schools have increased.

Twenty years ago state-educated girls were the strongest group, he says, ahead of boys from independent schools; now they are the weakest. This is true even in subjects seen as “female-friendly”, he added. “Girls were getting 25 per cent more As and Bs in modern languages in 1965; in 1985 this had fallen to 0.87 per cent.” The problem did not stop at A-level, either - boys’ lead widened further between A-level and finals.

He also said that neither boys nor girls from state schools were getting into Oxford and Cambridge in anything like the same numbers as 20 years ago, “The state system is increasingly sending boys and girls to the former polys; the older universities are becoming the home of the independent sector.”

He attributes the fall in state-educated girls’ performance, which was most marked at the end of the 1980s, to the abolition or merger of so many girls’ schools after comprehensivisation. The upturn in the early 1990s is due to the effect of GCSE, “which favours girls and gives them more confidence”.

On the subject of history, he said that “girls should be told” about recent research into the bias in assessment at Oxford and Cambridge. He said that examiners and tutors “were awarding high marks to flashy writers who boldly affirmed a particular view but could be disguising a lack of knowledge”.

These students tended to be male, while the more cautious and conscientious girls, who presented reasoned arguments backed up by evidence, were less highly regarded.