Here's my strategy:
My kids don't go places with people they don't know very well and I don't know very well. What I am teaching them is to be responsible and to value relationships with people who are also responsible.
My daughter has a boyfriend but they don't 'date'. He is like a member of our family and she is like a daughter at his parent's house. His parents are decent people... we don't hang out together but they live in our community and we've had several good chats with them. ANyway, the kids started out as friends a couple of years ago and have very slowly become sweethearts. They both recognise the value of going slow and maintaining their friendship because it's not like they can move out on their own any time soon. They've got a long way to go, and they don't want to risk screwing up the very good thing that they have. They've talked about all this stuff... they have a pretty realistic view of life and both of them want to avoid hurting each other. Sex is something that they want to save for later, and it's not a religious thing, it's a practical, sensible thing. If they end up having sex together when they are in college (and a bit more independent) , it will have been worth waiting for.
Anyway, he's a pretty neat kid... we took him on our family vacation and enjoyed his company.
She's 15, he's 17.