The whole business of girls' versus boys' attainment at school is a bit of a puzzle, really.
If anything, schooling styles have become less biased towards the "sit still, practice your writing, memorise everything...." over the last 30 years or so, so in theory, boys should benefit from that. But it's over the last 30 years or so that the attainment gap has tipped towards girls (it used to be that boys were always the higher achievers) and continued to widen in their favour.
So, what's causing the disparity?
One theory is that a lot of it is down to expectations. More and more, girls are expected to do better at school than boys, so they do. It's an example of stereotype lift. The positive reinforcement of girls academic abilities in school bolsters them up.
Meanwhile, boys get the opposite - they're now expected to do worse, so they do. It's stereotype threat, if you like.
Also, as high achievement during the school years becomes a largely female characteristic, guess what? It becomes devalued in the eyes of young males, as most "feminine" attributes are. So they're even less motivated to do well.
I think you'll find that higher up in secondary school, maths and science results still tend to be a bit higher overall for boys than girls (I'd need to double check that still holds true) and there you find the opposite situation: girls are stereotyped as being less able at maths/sciences (better at English/modern languages) and boys are stereotyped as being superior in these areas, so they are. Stereotype threat and stereotype lift again.
Plus there are still pervasive images of maths/science/technology being a haven for geeks etc. which has been shown to be massively unappealing to most girls (in the way being a "swot" is seen as being girly for the boys) so that's another off-putting aspect.
Thing is, girls have proved that one disadvantaged gender can massively catch up with the other, so the same must be true of boys. Question is, how to do it?