I went to a girls school and had male teachers, and my brother and friends went to boy schools and had female teachers. As far as I know, none of them posed any threat, and I certainly wouldn't automatically be concerned if I saw it happening today. I don't see why a teacher would be more likely to attack children if they were all of the opposite sex, is that usually the case? I would have assumed a paedophile teacher could be teaching boys, girls or mixed. I also don't know that the attacks need to be heterosexual; I think the stereotype is of a male teacher predating upon young boys, rather than girls.
Obviously, there are some teachers of both sexes who abuse the children in their care, sexually or otherwise. I think I've actually heard more about females doing it tbh, though I have no idea whether that's representative or whether it's just more likely to make headlines. Either way, I believe it's a very rare occurrence regardless of the sex of teacher or child, and though obviously there should be a determined effort to prevent it, I certainly wouldn't start assuming any teacher has bad intentions because of their sex, or the sex of their students.