Speaking from personal experience (as a white WC woman who over achieved with a brother who underachieved), I think the main reason is that education is not seen as important amongst most white WC males, they’ve heard their whole lives how their fathers, uncles, grandfathers etc had no qualifications, but had good jobs and supported families.
The main career option for them is usually to go into the trades (which is a lot less appealing for girls) where they can earn good money and can start off as labourers (not needing any qualifications). This is very common with the boys I went to school with and what almost all the men in my family have done.
There’s also the difference between the way boys and girls are raised, I was raised to be agreeable, compliant, conscientious, mature, independent, boys are typical infantilised and have excuses made for them, so they behave more poorly and are less conscientious and mature.
I don’t believe it is anything to do with schools apparently being more suited to girls, it’s that behavioural standards are much lower for boys, they have less respect for authority and do not value education because they have other career options that earn well which girls don’t have or are not appealing.