Girls-only success 'based on selection'
The findings seem to contradict the popular view that girls flourish if there are no boys to distract them or dominate lessons, and they can be stretched further academically.
The study, by Professor Alan Smithers and Dr Pamela Robinson, of the Centre for Education and Employment Research at Brunel University, supports their earlier investigation last year. This questioned the superiority of girls' schools in the league tables.
The latest research shows that the success of all-girl schools was less to do with gender than pupil selection. It found that single-sex schools tended to recruit from more favourable socio-economic backgrounds and had the benefit of long-established academic traditions.
The study also found that girls who went to single-sex schools found the atmosphere bitchy, spiteful and competitive, and would not choose the same form of education for their own children.
One respondent said: "All those girls together were so competitive. The smallest spelling test, and there was mass hysteria over what marks you got."
They admitted that having boys in the class would have been distracting, though there was no support for the idea that boys tend to dominate classes.
Those with experience of co-educational schools said that boys often diffused any hostility that existed among girls.
"When the girls did start getting bitchy, the boys could make a joke of it," she said.
Boys who had also experienced a single-sex education expressed reservations about sending their own children to similar schools.
Both sexes felt a mixed environment was more natural and enriching, and enabled girls and boys to form better social relationships which would prepare them for adulthood.