Well, here's an opposing opinion. Sort of.
As was mentioned, teachers are already overwhelmed, and I really do think this is an instance where the parent should be taking the lead. That said, I realize that for religious, cultural, and personal reasons- and yes, simply being uncomfortable about the subject), many parents do NOT give enough information. So- what happens when your beliefs conflict with what the school is teaching? IE-abortion, premarital sex, birth control, masturbation, etc? If you let the kid opt out of this at school, then who is the one who suffers? The kid does not get the information they need, and they are marginalized.
Of the kids who "get into trouble", I would love to see numbers on how much and what they learned in their sex education classes. I submit that the sex ed information- or lack thereof- too often is not the problem, but a lack of parental involvement/supervision is. I think these days, kids are much more aware of the consequences of unprotected sex- far more than when I was growing up. We were given very rudimentary info, yet I can think of only 1 student in my 4 years of high school who became pregnant, and this was in a school of several thousand.
These days kids are exposed to so much- TV, movies, etc, and there are countless instances of teen moms and their problems, STD's, and now we even have HIV and AIDS etc. We NEVER had movies or TV shows that discussed these things on a regular basis.
I think the attitudes of today's society towards sex is FAR more of a problem than a lack of available information and options, but that's just my opinion.