I really think education is key. Whether parents like it or not, teenagers are going to have sex. I remember what it was like in high school. I was a freak for being a virgin. Of course I didn't care. It was a decision I made because I was educated. My mom actually talked to me about it when I became a teen.
I can remember 3 girls getting pregnant while I was in high school. I guess that's not really a high number even though I went to a small school that averaged 300-400 students. Still.... There were also a few scares that I knew about, and overheard stories of what happened at parties.
One of my female friends had two pregnancy scares. The sad part is, she had no idea how her own cycle worked. She still doesn't, she thinks she got pregnant 2 days after she had her period.... I can also remember one of her uncle's girlfriends gave her a month's worth of birth control and she thought she was good for the month and didn't have to use a condom. I knew better, but it wasn't what she wanted to hear. I made sure to know these things so that if I ever did decide I was ready then if it was a girl I wouldn't get her pregnant.
My point is, it isn't wise to let girls like my ex-friend C run around eternally ignorant. At the very least she knew enough to use a condom, though I wonder if she went without anyway if she couldn't get one. I'm all for telling young teens that it isn't a good idea because I agree they aren't mature enough to make that decision. However, I am also not naive enough to bury my head in the sand and believe that teens won't do it just because we tell them not to. If they decide they want to, they're going to. And I think it would be an excellent idea to make damn sure that if and when they decide to have sex that one, they know how their own plumbing works, and two, they know about contraceptives and how to use them.