Well, I think basically that schools should stay out of people's personal lives, in that.. as an example, I don't think schools should teach religion or politics, or morals. Those things are up to the parents to teach, and instill in their children. That being said, while some parents will do that, there's a long stretch of children that aren't going to get that because they have parents who are struggling to raise them, working two/three jobs, and they don't have the strong social or homelife structure that they need, and I think schools end up playing a huge part in how our children are formed.
However.. I do think that options, and facts, should be taught. I think sex ed (not how to have sex, or this is how you pleasure a woman/man, etc), but this is what STDs are, this is how you prevent them, various birth control methods and the proper was to use them...and what their safety/effectiveness factor is. Sex education also teaches (at least my school did) what is inappropriate, when you should report something, what is considered to be harassment, molestation, etc.
In the case of sexual abuse or molestation, you can't *always* count on the parents or guardians to teach this. A very high percentage of sexual abuse occurs in the home. How can you trust a father figure to teach their child about sex if he's abusing them? I think some of this stuff is definitely something that should be taught. IMO, this is definitely something that should be taught by a third party and adamantly reinforced by the family.
I mean, my mom taught me as much as she could.. more about when I should or shouldn't have or decide to have sex. Of course she opted for the "don't have sex until you're really in love, and over the age of 90" tactic, but she did make an effort, but honestly.. my mother thought until she was an adult that you could get pregnant by brushing up against a boy walking down the hall or getting on the bus.. how on earth is she going to give me a proper education on STDs, pregnancy, birth control, etc? She did a decent job on the morality side of it.. but you know, my entire family with the exception of my sister and nephew are all old school. There was no one around for me, really, except my sister to teach me. My elder, very proper family knew nothing about it, really.
Fortunately I had the school and my sister is or rather was a proper hoiyden(sp.). Now she's a stick in the mud, but thankfully that didn't happen until after my teen years.