I've heard of that. I don't know what it is about schools thinking they should make kids stop masturbating.
In my high school, our sex ed teacher told us that you shouldn't masturbate because, and I quote as best I can remember, "If you pull out your own splinters, you know how to do it perfectly, and you get the splinter every time without any pain or effort. Then, when someone comes along and wants to pull out your splinters for you, he or she can't do it as well as you do it yourself, and it hurts, and it makes it where you just want to pull out your own splinters."
I was pretty baffled at her whole metaphor. First of all, since when is an orgasm like a splinter?