Please can you elaborate? I'm interested (sorry that sounds a bit sarky - I really AM interested!)
Sure.
This won't be in epic detail, purely because I can't squeeze an entire module's worth of work into a forum post, but hopefully it'll be a decent overview.
For starters, when you actually break down the stats of GCSE results, you find that it is considerably more complex than a simple 'girls outdo boys'. You have to take into account the differences in results between ethnic groups, socio-economic statuses and so on. Although girls do outdo boys in most cases, your socio-economic status is far more likely to affect your ability to achieve well at GCSE level.
You then have to look at the issue historically; this whole 'boys underachievement' thing seems to be quite new. It's suddenly exploded over the last few years, with a real air of panic about it. However, as early as the 1920's people said of boys: 'they're not slower than girls, it's just their age'. In 1923, the Board of Education wrote 'it's well known that most boys, especially in the period of adolescence, have a habit of healthy idleness'. In the 1940's again it was perceived that boys were behind girls and again, the excuse was made that it was 'just their age'. Throughout the ages, this idea that boys are underachieving has existed; it is nothing 'new' whatsoever.
From all the stuff over the ages, four main discoures have emerged relating to boys and education and underachievement:
1) 'poor boys' - notions that men have been victimised through feminist agenda (this has its theoretical basis in theories surrounding men's rights).
2) 'boys will be boys' - notions that psychological, and physical masculinity is something boys are born with, it is innate. This has led to theories of requiring more competitive sport and 'target setting' because these appeal to 'boys needs' and that also we need to give boys status to confirm their masculinity (this has its theoretical roots in evolutionary psychology).
3) 'Problem boys' - notions surrounding the 'laddish' culture and ideas that boys naturally adopt anti-social behaviours.
4) 'At risk boys' - boys are somehow disconnected from society, they have low self esteem and feel alienated from education
(Both 3 and 4 have their theoretical basis in ideas surrounding individualism).
This has led people to believe that schools have become feminised and are feminising, and that strategies to improve this need to be about reparing the male agenda, by having targets, reward systems, male role models etc.
But are boys brains really different to girls brains? Do they really think in a completely different way, or is this a social construction? Are there really different 'learning styles' for gender? Well teachers certainly appear to think so, with comments from teachers saying that boys prefer the quick, active lessons, while girls are quiet and prefer group work. But research by Coffield (2004) concluded that they could find absolutely no empirical evidence to suggest that implementing these gender based learning styles made any difference whatsoever. Sukhnadan (2000) believes that differing learning styles are more likely to be influenced by individual characteristics and abilities over gender.
Schools where social constructions of gender are less accentuated, tend to have a much reduced gap between the achievements of girls and boys.
It's also worth noting that despite all this moral panic, men still hold the majority of top exec positions, earn the highest wages etc etc.
There is considerably more to this topic, this really is the very basic outline, but hopefully it gives you an idea into some of the ideas around it.