All-girl schools could be pushed to the margins as pupils increasingly reject the “reserved” surroundings of single-sex education in favour of mixed classrooms, according to the editor of The Good Schools Guide. Lord Lucas estimated that fee-paying girls’ schools were in danger of losing a quarter of their British pupils over the next 20 years as part of a “gradual decline” in fortunes. He said schools had up to “up their game” by placing a renewed emphasis on subjects such as the sciences and engineering, which are usually seen as the preserve of boys, and commissioning new research to definitively prove that girls perform better in single-sex schools. It comes just days after a major report showed that the number of pupils in schools belonging to the prestigious Girls’ Schools Association dropped by 1.4 per cent this year. But leading headmistresses condemned the comments. Helen Wright, head of St Mary’s School in Calne, Wiltshire, said: “It is an old fashioned attitude. He seems to have an idea of girls’ schools that they are convent-style establishments from the 19th century.” Over the last 25 years, growing numbers of fee-paying boys’ schools have dropped their single-sex status to accept girls. Less than five per cent of establishments listed in last year’s edition of The Good Schools Guide were all-boy – down from a quarter in the mid-80s. By comparison, girls’ schools have been hugely reluctant to go co-educational. But it is claimed that the number of pupils attending these schools nationally is falling. According to an annual census published this week, 93,372 pupils were educated at 174 GSA schools this year, compared with 94,656 a year earlier. Speaking to the Telegraph, Lord Lucas, a Conservative peer who founded the Guide in the 80s, said: “I am absolutely not against girls’ education, or indeed boys’ schools, but it is something that’s becoming harder to defend and more of a minority thing. “Schools need to give positive reasons to choose a girls’ school. The old reason that without boys they can concentrate may be true for some girls, but most girls who grow up in a co-educational environment do pretty well and find they can manage quite happily. “The girls’ schools tend to be quieter, more reserved and less lippy but girls in a co-ed school seem to thrive on the rowdiness. “I question the old traditional arguments in favour of a girls’ school and I’d like to see something more fundamental and evidence-based and that would make a real difference to the choices parents make.” Lord Lucas was heavily criticised by girls at St Mary’s Calne after making a speech to the school on the subject this week. But he said that schools had to demonstrate “that their pupils were aware of, and equipped to deal with, the world of men, marriage and career”. He also said they should try harder to “liberate girls from the accumulated prejudices of their upbringing by, for instance, making it okay to choose physics or electronics”. But Hilary French, head of Central Newcastle High School and president-elect of the GSA, insisted parents valued girls’ schools. “Parents want an environment where their girls are treated as individuals not as objects, which is what inevitably happens a co-ed school,” she said. “Girls in co-ed schools are often concerned about the way they look. They don’t want to get too involved in games in case they get too sweaty and they don’t want to get involved in science or maths in case they are seen as cleverer than their boyfriend. “Girls in girls’ schools can be themselves. If you want girls to grow up to be leaders of society and be on FTSE 100 boards, they need the personal confidence to see themselves as equals.”