Wait, teenagers know about sex? When did this happen?

The Bush administration has been focusing on abstinence as the only one hundred percent effective way of preventing unwanted out of wedlock pregnancies. Spending federal tax dollars on preaching this message to minors is bad enough, in my mind, and the 18-29 year old crowd is being added as targets of this message since the problem of out-of-wedlock pregnancies for that age group is large. I see two logical flaws with this approach. One is that if abstinence is the only 100% effective way to prevent unwanted pregnancies, and pregnancies are a risk one takes when choosing to take part in unnecessary and risky behavior (sex, that is, if you don't remember what you learned in middle school health class), what is preventing that logic being applied to other unnecessary and risky behavior. High school sports come to mind. Any kind of contact sport (though according to my brother, dancing is a contact sport, football and lacrosse are impact sports) carries a risk of injury. If the only 100% effective way to prevent unwanted concussions and broken bones is to not take part in sports, why are these sports encouraged? I guess team-building and physical fitness are some of the benefits of doing sports; however, there have been a few studies showing that encouraging aggression on the field translates into more aggression in other aspects of life, so there is at least some detrimental social impact from sports like football, etc. In addition, frequent sex has been linked to improvements in mood and mental composure. What it seems to boil down to is that society deems sex out of wedlock to be immoral, while sports to be wholesome, to hell with the evidence. This argument could be continued indefinitely, it seems, and probably neither side would be able to convince the other. So even though the internet is the perfect place for such an indefinite argument, I'm not interested in having it. So on to my main objection (math warning).

In practice, abstinence is 100% effective, while contraceptives vary in effectiveness, but tend to be good and can be combined (if a condom is 90% effective, and the pill is 98% effective, a combination of the two should be 99.8% effective.) Abstinence is in the lead. However, public policy is not directly tied to sexual behavior. There is a barrier: the effectiveness of education. Assuming that abstinence only education is 90% effective, and contraceptive education is 95% effective (both probably off, but in my mind fair guesses), then we have to tie in these numbers to get the actual expected risk to the population. With these numbers, abstinence only education would be, in the end, 90% effective (90% of the time it works every time, 10% of the time it never works), while contraceptive education would be 94.81% effective (95% of the time it is 99.8% effective, 5% of the time it never works.) While touting the message that abstinence is the only 100% effective behavior to prevent unwanted pregnancies, it may be the case that contraceptive education is more effective than abstinence-only education (using my numbers and a slew of other assumptions.) So until we know the effectiveness of the various methods of education, relying on the assumption that people will behave in accordance to whatever way we educate them is unfounded, risky, and may lead to a less effective public policy towards sex.