I was a New Year's Eve accident...but my mom always made sure to tell me that I wasn't a mistake.
I think teenage pregnancy is due to a combination of factors--bad parenting, curiosity, sex in the media, poor sex education (at home and at school), genetic defect, etc.
I've always found it interesting how much the US loves sex, yet still seems so unwilling to talk about the issues that surround it.
We look at the people who talk about the joys of sex as naughty or a bit kooky. And when people preach abstinence only, it just doesn't register like it might have back in the day.
FNF touched on this, but I think we need to be more open about it, we should push contraception more and we need to stress how serious having a child is, and how dramatically it can alter your life.
I'm lucky...my parents didn't tell me shit about sex, so I had to learn by book. That, and I had the sense to know that I didn't want any kids at such a young age. Though I think my education played a role as well.
If I recall my days of sociology class...or maybe it was one of my psych classes...anyway, the concept/theory/study/whatever was that the more educated you are, the more money you make, and the fewer number of children you have. I don't know how solid this is, but it seems to be the case (with exceptions of course). Based on this, it would seem the best place to start is in the classroom (though parents should take charge in the end).