I've already posted my views on sex education on a thread about that topic. To give my views in a nutshell, I believe it should start young. When I was going through schools, I did not get any proper sex education until I was 16+, and even then it was really just scare-mongering - the kind of education that said if you have unprotected sex you'll get every horrible disease known to man and end up as a single parent with a poorly paid job. It was like those adverts aimed to keep kids of drugs. They give you no information, but just said "Sex --> Evil --> Don't do it'.
I'm probably being a little unfair, but I felt that the detail sex education talk should have come much lower down the school. Even at the age of thirteen, children are becoming sexually aware. I know that some parents don't want schools to make condoms available to children under sixteen because it encourages them, but think about it. Would you rather your kids were having unprotected sex? If a kid wants to have sex, it will do so regardless of what you tell it. I think it's best for them to have a place where they can easily get free condoms for, because it's better than them contracting STDs or becoming pregnant.
If I had a kid who was starting to show an interest in the opposite sex, I'd make sure they knew all the facts and I would make sure that they carried a condom with them in their wallet. I would make sure they knew I did not approve of underage sex, but I'd want them to be safe if they did ignore everything I'd told them and do it anyway. Condoms were not available to me for free until I was a university and I found this shocking. By the time most people go to university at 18, they've already had sex at least once.
That's my argument, anyway, and I'm sticking to it. Condoms should be available in high school, as should detailed information about sex.