I'd dispute that. When my mother was in high school, students were allowed to leave the premises during lunch hour if they chose, and many did and went to the local burger joint instead of the cafeteria. Nowadays, even when students have nothing but study hall for the last period of the day, they're not allowed to leave before the closing bell.
What does any of that have to do with sex? Not much directly. But it does speak volumes about society's attitudes toward absolute control of the "helpless" youth. It's a small wonder then, that personal responsibility doesn't exactly thrive in such an environment.