Girls who attend single-sex schools leave with top grades but may be at a "huge disadvantage" later on if they are unable to talk to boys, a leading headmaster has suggested.
Richard Cairns, head of Brighton College, said young women could face difficulties if they do not learn to socialise with the opposite sex as children.
In an article for the magazine www.independentschoolparent.com, Mr Cairns took aim at single-sex schools, saying he was puzzled by parents looking for a place that will prepare their child for the future who are swayed by "outdated notions" about young women performing better in girls-only schools.
"All parents looking for a school for their daughter have broadly similar criteria in mind," he wrote. "They want somewhere that readies their child for the world beyond the school gates, academically and socially.
"That is why I am often perplexed when they end up being swayed by outdated notions about girls performing better in single sex schools and plump for that deeply unrealistic world.
"After all, if girls do not learn to socialise with boys as children, what happens when they go out into the work place? They may have a clutch of A*s and a first class degree but if they cannot meaningfully converse and communicate with male colleagues they will be at a huge disadvantage."
Supporters of girls' schools argue that students achieve high standards, and are more likely to take subjects traditionally seen as "male" - such as physics and maths.
Caroline Jordan, president of the Girls' Schools Association (GSA) said it was "old-fashioned" to assume that these schools do not offer plenty of appropriate opportunities for young women to interact with young men.
In his article, Mr Cairns argued that girls at Brighton College - a co-educational private school - would not say that they have been held back by learning alongside boys.
He went on to acknowledge that there are many good schools that are co-educational and many that are single-sex.
But he added: "There is something, I feel, much more common to schools that educate both boys and girls and that something is kindness.
"Boys in single-sex school tend to create their own artificial hierarchies where only those in the 1st XV rugby team are truly valued while girls-only schools sometimes suffer a degree of emotional intensity that can lead to bullying.
"Contrast that with a co-educational world where girls admire the boys who dance, sing or act, and so, therefore, do the boys. Contrast that too with a mixed environment where the emotional intensity of all girls is diluted by the boys.
"In other words, there is a place for everyone and an environment where girls and boys can be themselves."
Mr Cairns went on to say that research in the UK and abroad has "cast serious doubt" on the argument that girls do better academically, particularly in more "male" subjects when they are not close to boys.
"The real reason some all-girls schools have a strong track record in traditionally "masculine" subjects, such as physics, is that they're very selective institutions," he suggested.
"Bright girls are more likely to study physics than those of average ability. Whether they are sharing classes with boys is largely irrelevant."
Ms Jordan said: "Whilst Mr Cairns may find it unpalatable, the truth is that girls' schools feature heavily at the top the league tables for independent schools and have done for decades.
"It may also have escaped his attention that all girls' schools provide plenty of appropriate opportunities for interaction with boys; in fact, it is rather old-fashioned to assume anything other.
"Finally, it is not just the 'brightest' who do better at STEM in girls' schools - a recent and extensive survey by the Institute of Physics found that girls in independent girls' schools are 1.5 times more likely to study A-level physics than girls in independent co-ed schools.
"It is time for Mr Cairns to cease his rather tiresome attacks on independent schools colleagues – the sector benefits from diversity and choice and I am sure he would agree with that."