******** should learn around 11-12yrs old. Truth MOST have already been exposed to it in some form or another;classmates, friends, media, books left unsecured, newstands, internet, tv shows, their own developing body which is happening younger and younger in girls ~ (I believe because of all the hormones they consume via food)
It should be done in a straight forward scientifc manner and segregated. I think young boys, as well as girls, are embaressed and uncomfortable about the changes going on with their thinking and bodies;less likely to ask questions. More likely to poke fun to hide their feelings if the opposite *** is sitting in the classroom with them. Let them submit anonymous questions that can be answered at a later time. Probably uncover any suspicious activities, save a mind or two.