A lot of teenagers want to start a family and know perfectly well how to use a condom
As a society we have actually created the problem by stigmatising teenage pregnancy. It doesn't conform to socioeconomic norms of educational and economic success thus it is wrong. By making it 'wrong' teenage mothers are marginalised and often receive poor antenatal care and fewer opportunities for themselves and their family.
There were actually more teenage mothers in the 1950s than in the 1990s. Of course in the 1950s it was acceptable to have a baby under the age of 20 (as long as you were married). I am not advocating forced marriage but the fact that society accepted it meant teenage mothers got a better deal (in terms of their image anyway)
Define teenager. There is a big difference between a 13 year old who does fall pregnant accidently through poor knowledge and a 19 year old who chooses to start a family young, but doesn't expect to be judged just because she isn't fulfilling society's expectations.
We are not going to stop teenage pregnancy. There are much wider socioeconomic, psychological and political issues surrounding young motherhood than sex education.
Personally I would be more worried about STDs and the damage to young people's health, this is where sex education should be aimed at.
I am sure teenage motherhood is tough and there are issues about the welfare of young mums and their babies but to conclude my point, it is society that has caused such issues. I am also sure that there are many great young mums doing a better job than older mothers.