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Clever girls, stupid boys. That's become something of a modern educational orthodoxy, as girls across the developed world are more likely to get top exam grades and university places.

The gap is so great that the UK's university admissions authority has warned that being male could soon be seen as a new form of social disadvantage.

In the UK, the gender gap between men and women entering university has never been wider. In a remarkable statistic from the Ucas admissions service, the gap is more than 50% in a quarter of parliamentary constituencies. And no doubt this disparity will play out over future generations.

But hold that bandwagon there.

Because a global study from the OECD, based on more than 60 countries, has thrown up some very interesting challenges to generalisations about girls always doing better than boys.

Teacher bias

First of all, it suggests that school systems give greater rewards to girls rather than boys, even when pupils are of similar ability.

Teachers are more likely to "mark up" girls' work, says the study. It suggests that this leniency in marking is an unacknowledged reward for girls being more school-friendly.

Image copyright Thinkstock Image caption Women are much more likely to go to university than men

Girls are more likely to be better behaved, more likely to get homework finished, less negative about going to school. And even when boys' work is just as good, the higher grade is more likely to go to a girl.

Where coursework is important to grades, could this have an influence on results?

The study also shows that in science and maths, boys are likely to be at either extreme on the ability spectrum.

Among the lowest achievers, boys predominate. It's an international pattern, with boys much more likely to be among those who get the worst results, drop out and leave education unskilled and poorly qualified.

But boys are also right at the top of the scale too, occupying more of the places among the very highest achievers.

Computer games 1 Homework 0

The biggest gender gap in school is usually associated with literacy, with girls runaway leaders in exams and international reading tests.

But the OECD has come up with the unexpected finding that this advantage in school does not last into adulthood. When young men and women get to the end of their twenties, their reading skills are not that much different.

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The study also has some nuggets about the influences that shape how well pupils do at school. Girls do much more homework than boys and this has a direct impact on results.

Boys are much more likely to spend long hours playing on computer games and this can have a direct impact on the likelihood of doing homework.

But there are a couple of big conclusions delivered by the OECD's education guru, Andreas Schleicher.

There is no "maths gene", there is nothing inherent about boys or girls doing particularly well or badly in different subjects.

If boys can do better than girls in maths tests in some western countries - and then girls in Shanghai can do better at maths than those western boys, it shows the variable factor is not gender, but those education systems.

Mr Schleicher says the study shows there is nothing innate, immutable or inevitable about gender differences in education.

There might be a blizzard of overlapping influences - self-confidence, parental expectations, society's stereotypes, gender bias, school support - which can affect how young people behave.

But it's nothing that is hardwired by gender.