All schools should teach kids about sex just like they teach traffic safety and first aid. Sex ed should not be compulsory like all other subjects as the children whose parents will not sign the permission slip are likely to be the ones who knows the least about sex in the first place.
Sex ed should of course teach the biology about it all, the various means of contraception, and how to use them, tell about different ways of sexual practices and orientations, the emotions connected with sex and answer any sex-related questions the students might have. Handing out condoms is also a good idea since many teenagers are too embarrassed to buy them themselves.
A good way to do sex ed is to have guest teachers do it. When I was in high school we had two sex ed volunteers come and talk to us and it was really great. It was a man and a woman who were both in their 20's and it was much better than it would be to have our teachers who were at the age of our parents do it. They also taught us how to use a condom in the most obvious way possible; they gave each of us a condom and then passed a pink dildo around class where we had to put our condom on it. It was great fun and nobody became sexual predators for that cause.
What is so wrong about teenagers having sex? I don't get it. Sex is one of the few things that is both fun, healthy, and free. As long as everyone involved consents and respect each other's boundaries what harm can be done then? Inducing guilt in young people for having sex is far more harmful in my opinion.
When I have children one day I'll hope that they'll have lots of good sex once they feel ready for it.