This broad brushstroke is so unfair. What public school district are you specifically talking about? I've seen a lot of curriculums and haven't found your assessment to be true at all. Having taught for 33 years, and my husband teaching health for 33 years, this was not our experience. In the district where we taught (a public school system) parents came for meetings to view, discuss, and sign a permission slip for their child to be in class or to opt out and not have any part of the program. The curriculum was written by parents, teachers working together.
The messages children learn in school are far less important than the messages they receive from their #1 supporter - YOU, the parent. The situation with Palin's daughter is a "teachable moment." Any parent who doesn't want a teen pregnancy for their child should take this as an opportunity to get a conversation going or to continue one.
As for teens who do get pregnant, please don't dump that burden on the schools. The last time I looked this up, research said the average father spends less than 10 minutes per day in meaningful conversation with their children. This doesn't include: clean your room, listen to your mother, do what I say. Hang-outs? If your child is hanging out where you don't think they're safe and the environment is healthy, how is that the school's fault?