I'm fairly equivocal on this, but MoonCake: boys and girls are different. In some ways because they're socialized to be so (which is gonna happen whether they're educated together or not), but there are fundamental, honest-to-God biological differences. Boys will make jackass comments anyway. Girls will be snotty to boys anyway. This doesn't prevent them from socializing outside of school (see also: homeschoolers who are active in their communities; I hear those who go to same-sex also still manage to mingle with their opposite-sexed counterparts). You paint a nice slippery slope, too: kids aren't stupid, and even if they couldn't understand (and still cared) about the separation, you educate them to be respectful of everyone anyway, like you're supposed to. But no, oh my god, of course educating boys away from girls will lead to a regression to Neanderthal manly behavior.