Obviously when stuff like this comes up people will look at all different factors.
Labour's response to this previously (when looking at Labour's Mayor or London) has been to run adverts asking men not to do stuff; the "Maaate" adverts, the "starring is a sexual offence" adverts, and not a lot actual measures put in place like more security at stations etc. It seems that the only men receptive to the messaging were the decent men who weren't/aren't sexual offenders, whilst the actual offenders just ignored the messaging.
My concern with doing lessons in schools, would be that the truant children who most likely would go on to be sexually aggressive won't actually be there to get the lessons and you do run the risk of resentment from others.
I think there's got to be a better way to through to those who will go on to offend.
I suppose as people have said it's a lack of role models, and I think it's more productive to give people examples of how to behave instead of how not to behave. Be positive, not negative.
It's not unusual for children to go through primary school without coming across any male teachers, and for boys from single parent families that's quite a miss.