The problem with sex, is that its somewhat taboo in the older generation. Most parents seem to expect the school to have sex-ed classes, because of the awkwardness of talking about sex with your children (and kids to parents). However, you never know who teaches your kids sex in school, and what their views on sex are. Look at all those crazy "You need to save yourself for marriage!" people. You wouldn't want them teaching your kids about sex, would you?
From the moment people mature enough, they'll have sexual feelings. That doesn't necessarily mean they're ready to have sex. I think its important for the school to have sex-ed classes, but the parents need to talk to their kids as well. While they shouldn't say sex is GOOD to have when you're 12, they need to say that its a natural thing. Not encourage, but teach, and tell them the importance of using protection. No matter how awkward it can be.
People always want a scapegoat. Sadly, most people use the television as a scapegoat. But the television is not to blame, the parents are. Sex isn't as taboo in the younger generation. People will talk to their friends about how they got laid etc, and if someone haven't had sex, especially among guys, there's a chance they'll feel like an outsider and rush things. Its the very same thing as cigarettes and alcohol among the younger people. If everyone talks about it, true or not, there's a chance other people will do it or use it as well, in order to not be an outsider, which is the number 1 fear across the world.
Additionally, if adults try to make something out to be forbidden, people WILL try it out, not only to see WHY its forbidden, but also to rebel against their parents. So no, the school or the television is not to blame. The parents are. Like it or not.