In the classroom setting, I don't discuss contraception. But I do encourage the kids to discuss it with their parents. If they want to talk to me one on one, I will do that. But since I do not agree with sex outside of marriage (and I don't feel that God does either) I don't give the "but if you are going to anyway" speech.
Some of my thoughts on sex:
Sex is a beautiful thing, created by God, not only for procreation, but to build an intimate bond that He intended to be only shared between husband and wife. In the right setting (marriage) sex is amazing, healthy, and positive. In the wrong setting it can be a negative experience: lead to disease, unwanted pregnancy, emotional scars, among other things.
By God's design I think it is best to wait til marriage, and I share that with my group, both in the classroom setting, and by my own life example.
I don't think one is doomed to hell for all eternity if they have premarital sex, I just believe that they are cheating themselves out of the best that God has in store for them and their future spouse.
While I understand that it is hard to be an abstinent teenager, it is absolutely possible to survive the teen years without having sex (and again, I lead by example.)
I do realize that some teens in my group may have already had sex, and if so, I know that God is a loving and forgiving God, and He is able to help them if they desire to recommit their bodies to Him and save themselves from this point forward.