[roguecoder]

It depends on which society you are in; the more gender-equal, the better girls perform in school. There are places where they do slightly outperform boys overall, including in many colleges. The broader trend is that girls' test scores have been improving much faster than boys have over the past 40 years. It isn't that boys are performing any worse than they were before, or are being ill-served by school, it's just that girls have overtaken them. This change mostly came when standardized testing came about and grades were no longer subjective: with clear goals and unambiguous feedback, girls had new opportunities to excel. Boys, on the other hand, aren't socially rewarded for working hard on things they aren't good at, for empathizing and thus developing social intelligence (which is enormously valuable in school and particularly test performance) and weren't driven by the same fear of failure: worst that happens to me is I end up in my parents basement failing to pay child support.

(Your proto-bell-curve explanation has been mostly dismissed at this point, just like all the rest of the "variation" arguments: variation ends up being highly influenced by social and cultural factors. The variation in American boy's performance in school, for example, is partially a product of how shittily our schools serve poor African-American boys.)