Of course girls massively out-perform boys at GCSE! The GCSE was devised and implemented (implemented, lest we forget, by Margaret Thatcher) purely and precisely to ensure that this would always be the case, ostensibly as part of making schools "girl-friendly". But schools were never "girl-unfriendly": girls always slightly out-performed boys at examinations taken in the mid-teens, and they always will.
Meanwhile, A-levels have been made increasingly like GCSEs, to the same end and with the same result, while the curriculum further down the age range has of course been altered in order to prepare pupils for GCSE. But none of this proves anything except that a system contrived to favour very heavily one sex (the one that always did slightly better anyway) over the other is doing precisely that.
This is the key to understanding why thousands of boys did not used to leave primary school, nor did anything like the current number used to leave secondary school, unable to read. And it is also the key to the alleged superiority of single-sex girls' schools, most of which are in any case academically selective, socio-economically selective, or both.
Is it possible that the reason boys now do so much worse than girls at, for example, English Literature, even though most English Literature properly so called was writtten by men, is because the same people who created the above situation have also given effect in schools to their strange theory that works have been denied canonicity because they were written by women (Jane Austen? The Brontës?), rather than simply because they were not as good as those included in the canon. The latter are still taught to those people's own sons and daughters alike, at enormous cost in terms of school fees or wildly inflated house prices.
And just how hard could it be to examine everyone both by coursework and by final examination, simply awarding the lower mark as the final grade?