Put a bunch of teenagers in a room and talk about how not to get pregnant, what do you think they will be thinking about the rest of the day (at least).
Sex ed , IMHO, should be taught at home, not at school.
It is not the government's job.
You're kidding yourself if you think teenagers aren't thinking about sex at least 50% of the time anyway, mate. Sex ed is not going to increase that, it will only give them a clue.
Also, sex ed shouldn't just be about contraception it should also go into graphic detail about sexually transmitted infections. It astounds me how little people know about what you can catch, how you catch it and what (if anything) you can do about it.
If horny kids were armed with the full and correct information about STIs they may think twice.
Leaving it up to the parents may work for the level-headed and educated parents but let's face it.... there are just way too many idiots with reproductive organs out there.
Kids should not be disadvantage by having prudish or stupid parents. Those kids will be the ones that get herpes or get knocked up.