It is a claim almost universally accepted that girls thrive at all-girl schools while boys do better in a mixed environment. The theory remains unproven but is one of the reasons for the current parental stampede for places at all-girl schools.
This, along with concerns about boys' continued underperformance, has led Barnet - one of England's top five education authorities - to pilot single-sex teaching in its mixed schools.
Nationally, a few isolated mixed schools have separated the sexes - mainly on the instigation of individual headteachers attempting to raise boys' achievements - but Barnet in north-west London is the first to consider an authority-wide policy.
One of the borough's schools - the grant-maintained Mill Hill County High - has quietly been operating its own version of the single-sex scheme and believes its combination of mixed and single-sex tuition is maximising pupil potential. This is borne out by figures showing that the number of pupils getting five good GCSE passes has risen from 40 per cent to 69 per cent in the three years since the scheme was introduced. That's well above the 53.4 per cent average figure for Barnet which put the borough fourth in this year's GCSE league table.
The project began in 1994 when head of science Chris Matthews became concerned that 20 per cent fewer girls than boys achieved a C grade or above in science GCSE. Three years later, the girls are 1 per cent in front of their male classmates. "Achievement has gone up for both sexes but girls have made a rapid improvement and are now out-performing the boys," she says.
Now almost all GCSE science classes are single sex, apart from a mixed class in each year which makes up the numbers.
Pupils study science in mixed forms for their first term at the school, and are then streamed and split into single-sex classes. Teachers adopt a slightly different approach when working with the all-girls' class, while changes in the national curriculum have allowed more opportunity for discussion in science lessons and more people-orientated topics.
"We have had to change our teaching style so that there is more group discussion. Boys like a direct challenge - 'I bet you can't do this' - but if you challenge a girl she will say 'I know I can't'. Girls need to be supported and encouraged rather than challenged, which turns them off," says Ms Matthews.
In English the boot was on the other foot, with boys trailing behind the girls. Head of English Mandy Watts says: "English is a subject where girls normally do better than boys. Boys prefer practical work involving problem-solving and finding a definite solution. Girls like to explore their feelings.
"It sounds a stereotype, but that is what happens. Boys like non-fiction while girls read fiction more willingly."
The problem was how to transport those ideas into the classroom. The first all-boy class was formed in 1995, with the remaining male pupils spread evenly among the mixed classes, ensuring the girls were never a minority in any class. Ms Watts says: "Boys don't have a problem with being in the minority. It only becomes an issue when girls are in a minority. Then girls underperform in comparison with groups with a better gender balance.
"Now we try to make sure that girls are never in a minority. Boys do well in mixed classes and have their performance raised by girls' presence. Girls are more attentive. "
Ms Watts believes the whole year thrived because of the better gender balance in their lessons.
Mill Hill County, like many of the borough's schools, has many more boys than girls. Creating a class for 30 boys meant girls were no longer a minority in the rest. The 14- and 15-year-olds from this pilot study took their GCSEs last summer and the results showed an improvement across the board.
In the mixed classes, the different learning styles of girls and boys is recognised and reflected in a choice of books which allows boys to study books they are interested in.
Different methods are employed in the all-boys class where Ms Watts admits boys can be at a disadvantage. "In discussion groups, boys tend to work to the lowest common denominator. If you're discussing racism, boys can be almost bigoted. Girls tend to balance their arguments, which is something the boys miss out on if the girls aren't there. The slight disadvantage is that you only get a male perspective. But the teacher is there to supply the breadth of argument the girls would have." The class is always allocated a male teacher so that boys have a positive male role model in English lessons.
Ms Watts adds: "The boys knew they were part of an experiment, which they found exciting so they worked hard. We felt that English should give boys a positive message. Too often boys feel that it is a girls' subject.
Two all-boy classes are now being run, concentrating on improving the performance of middle-ability boys and hoping to raise D grades to Cs.
The school says it is too early to conclude that the single-sex experiment has produced a long-term rise in exam results, but Ms Watts is sure it has improved classroom behaviour.
There are no plans to introduce all-girls' English classes. "They do so well anyway. Their results are much higher than the national average."
In science the change in the classroom atmosphere has also been dramatic. Ms Matthews says: "The girls are much more willing to have a go. Staff were able to spend more time with them than before as boys take up more of a teacher's time.
"Last year the lower ability group really enjoyed their science lessons. They were never going to get grade Cs, but they enjoyed doing experiments, got more out of the lessons, and had a better classroom experience for being in a single-sex group because we could spend time with them."
But even Ms Matthews admits there is still a long way to go: the project has not yet led to an increase in the number of girls taking science at A level - it is still regarded as very much a boys' subject.
Pupils from the all-girl group agree about the benefits of a boy-free class. Elisa Roth, 15, says: "Boys like to show off. They used to mess around, so we probably get more done without them. "
But the girls are all adamant that they don't want to go to a girls' school. Laura Sterling, 15, says: "Boys have different opinions to girls which, makes the lessons more interesting."
Headteacher Alan Davison had already been involved with gender issues as part of a #163;20,000 research project at his previous school in Essex. "It is not surprising to find that girls and boys are different and that they do not work in the same way. Our brains are different and it is crucial that we in education recognise that. Girls are more language-based and boys are more speculative. It is inate.
"But the data so far is inconclusive. I believe that totally single sex education is damaging because you are not getting the other experience, just one learning style. With a mixture of learning styles, boys get the reflective aspect and girls the speculative. Boys do better at A-level because they are more speculative. The best way for girls to learn to be speculative is from the natural speculators - boys. You need a mixture of these things."