First of all, I say start as early as possible. Most teens have sex out of curiousity, or are dooped into it like my best friend was, because they're uneducated. It'd be much better to teach them about sex, than the streets. The best way to talk about it is with an open mind. Make sure they're educated about STD's, as well. The pictures of what they look like scared me off for years. While you're speaking, you need to show respect to your teen, so that they're inclined to respect themselves. I'd start the conversation off asking what they've heard on the streets and in school about sex, and then take it from there, starting by correcting the wrong statements (there will be some). You want to be completely honest about the good and the bad of having sex, especially about teenage sex, and make sure that virginity is a respect for yourself thing. Good luck!
at 9:03 AM on Feb. 7, 2009