Even the high school kids know very well the impact of drug and sex. So if a teen claims he/she can't 明辨是非, it is usually a lie. However it is true some teens can't control themselves well. But more often than not, it is their conscious decision to go for the experience.
Once they go to college, there is not too much parents can do to stop them from experimenting their lives. In my opinion, the best thing a parent can do is get them to understand the impact of their action, and hope they will make the right decisions.
