It's certainly not a lack of education, but it's how the education is presented. Drugs are made to seem like a *gasp!* big deal. When really, a good many of them are not so much a trouble with responsible use, but the constant throwing down the dangers and taboo of illegal drugs unintentionally adds an allure to kids. Plus, not to sound like too much a cynic, but teenagers are pretty damn stupid.
Then again, a few illegal drugs when used responsibly can lead to a pretty good time and no bad effects, there's simply no grey area here.
Probably why Catholic schools have the highest teen pregnancy rates; they have no proper sex ed curriculum and kids are told that sex is bad and a sin. Which probably creates a reverse psychology effect. I should know this, I went to one, certainly didn't stop my classmates from screwing around.