Researchers have found that sex ed delays teenagers from having sex. It seems to be irrelevant what sort of sex education it is, as well.
Everyone else may be baffled by this, but I know why. When I was a teen, I found everything taught to me in school to be dull and tedious. For example, I loathed Jane Austin for years as she was required reading in the ninth grade. If you teach teens about sex, they will believe it to be dull and tedious.
Maybe we ought to teach them about drugs as well. Require instruction in Heroin and I can practically guarantee no one will ever become a junkie.