It seemed to me many years ago that there was an odd pattern in the schools, perhaps exaggerated in Catholic schools, but probably present in the public schools also. In the earlier grades, the girls, who sat still better, had better small-muscle coordination, and were more verbal sooner, pulled down the As, while the boys did more poorly. Somewhere in the middle school years, neat handwriting counted for less, and the boys started to catch up on other fronts. The girls, not always unwillingly, fell back. A cousin of mine infuriated me by saying that she got Bs in high school--boys didn't like girls who got As.

But, as they say on HN, the plural of anecdote is not science.