Religion or teaching abstinence does not prevent teen pregnancies. Studies have shown that. What does prevent teen pregnancies is good sex education and easy access to contraceptives. Fundamentalists believe that teaching the truth about sex will make children have sex. That's silly. The children who want to have sex will do so whether they know the truth or have access to contraceptives or not, and the ones who don't want to will not be bolstered by preaching at them.
I don't think teens having sex is a very good idea, but I don't think it's a sin either. And I would rather my child be taught the truth and have access to contraceptives, than to make life a lot harder by having a teen pregnancy. But then I think my children are more important than any religion. And I think we could go a long way toward solving the problem of teen pregnancy in this country if all parents thought that way. If a loving god did exist, wouldn't he/she agree?