It's BS. I think some schools do this for a few reasons:
1) Religious views (especially when it comes to the South--not supposed to have sex until married, so let's just tell the kids Not to do it no matter what)
2) No funds (no money to really expand the health portion of the classes, so they just give a basic "don't do it" speech)
3) Responsibility of the parent (some schools think it's the responsibility of the parent and not them that is to teach about sex--some parents think it's the school's responsibility instead!)
It's sad, really, how kids aren't educated well on the matter. I remember being in the South to see my now ex graduate, and I saw so many teenage girls with kids it wasn't even funny. I honestly felt sick to my stomach.
When i was in school, I didn't feel ready to learn about sex, sex ed, etc. It was seen as a taboo subject in my family and the thought of me having it made me sick and afraid and the idea of me having a bf at the time sent my dad into a rage. So I opted out of the classes. BUT I did do independent study about it all when i felt ready. And I learned later that all the classes did was talk about it scientifically, like how babies are made, meiosis, etc, and not really about the sex part. Which looking back I think was wrong. It makes me wish at times i could volunteer at a local high school and help teach these kids something. I'd probably feel a little embarrassed about it, but at least I'd feel better knowing that teenagers would be getting some much needed information.
Also, personally, i think to help counter this a bit, I think the age at which to buy sex toys should be lowered. i feel that if kids, especially females, had access to some toys, they might not be as inclined to jump into having sex if they can please themselves.
Just my two cents.