I'm not saying all males put on pseudo-masculine efforts, I'm saying it only takes one kid who makes an inappropriate joke like changing "public void" to "pubic void" when we're doing a code review. In such a situation, the boy will suppress a smile while he innocently exclaims he made a typo, while his friends all giggle innocuously. If you don't work with kids, you will not fully understand how the adolescent mind manifests itself in the classroom environment, and how difficult it is to suppress it. In the situation I just described, all we can do is mentally make a note to not call that same student up again. And in this situation and all related ones, we're dealing with a male student. Girls simply don't find stupidity that funny, and as an instructor I get pretty sick and tired of it.
I've spent the last 30 minutes defending myself on HN so I will conclude with this. We are not segregating our classes. We are not trying to shield female students from the realities of the world. We are simply making a business decision to offer an alternative environment for our female students who would otherwise have to deal with awkward situations like the one I just described. The all-girls classes are ridiculously chill and my instructors leap at the opportunity to teach them, because girls in middle and high school are on average more attentive and respectful than their male counterparts. You can tear apart my real-world observation all you want, but that is the simple reality of it and once you open your mind beyond some idealistic vision of what education should be, you'll understand that my reasoning is not just "unconscious sexism".