THE principal of Cheltenham Ladies' College has described single-sex education as a "winning formula", despite evidence showing the popularity of all-girls' schools is declining.
The latest edition of the Good Schools Guide, out tomorrow, includes the lowest percentage of single-sex girls' schools in its 25-year history.
Thirteen girls' schools that appeared in the first edition of the guide have been forced to close or merge.
Cheltenham Ladies' College was founded in 1853 and today educates about 865 girls aged 11 to 18. Principal Vicky Tuck said the proof of a good school should be the pupils that emerged from it.
She said: "Our focus should be on the pupils that emerge from the school, not what the school claims to offer."
Mrs Tuck said there was "something special" about the nurturing spirit of an all-girls' school.
"Our staff focus on excellence for our students, first and foremost – the fact that we only educate girls is not what preoccupies us," she said. "The fact that they do so well suggests that it's a winning formula worth preserving."
Janette Wallis, a senior editor of the Good Schools Guide, said the all-girls schools that have remained are the "cream of the crop".
"They really are stronger than girls' schools were 25 years ago. A lot of the deadwood has been swept away," she said. "Cheltenham Ladies' College is a great example."
Dr Alex Peterken, headmaster at Cheltenham College, which is co-educational, said there was no firm evidence that boys and girls did better when they were taught apart.
He said: "School is a preparation for life, and life is co-educational. Learning to live, work, interact and socialise with members of both sexes is all part of the challenge of adolescence."
Outside of the classroom, he said co-education was fundamental to students' social development.
He asked: "How can a single-sex school stage a variety show, school play, debate or concert with quite the same real-life sharing of experience and teamwork as a co-educational school can?"
"And perhaps most crucial of all, how many all-girls schools can provide their pupils with the opportunity to lead and manage boys?"