The 6th graders I teach fall into two categories: Those who value an education (due to their upbringing, realization that education means more bucks, or learning from another's mistakes) and those who don't care and, ergo, don't try. The boys far outsprint the girls in Math. It's about 50/50 in science, since there's so much that needs to get into their heads, and a lot of that comes from the book. Boys are better than girls at getting things done problem-wise. Girls are better at figuring out language, since their brains are wired that way.
The girls whine more, cry more, get moody more, and get nailed for useless jibba jabba. The boys get nailed for name calling, body noises, and laughing, the same kinds of stuff my peers and I got nailed for at that age.
Is there a bias? Heck, yeah. See it every day in wimpy, watered-down reading books, in more girls than boys in the activities, all that stuff. Can it be reversed? Yoobetcha, but only when a$$hats like the AAUW and their associated vaginas are silenced. Till then, the war against boys continues....