We have teens and tweens. This is a big issue in my house right now.
I would never advocate abstinence-only education, but it's common sense to make it a priority say to young people that the only way to make 100% sure that they will contract neither children nor a disease is to refrain from sexual activity.
I think both sides go about it wrong. Abstinence advocates (mostly Christians) tend to romanticize sex, albeit inadvertently. "Save it for someone you really love and want to be with forever." Worst possible thing to say to a teenage girl, let me tell ya. Sex ed advocates tend to over-focus on sex itself and not on the long-term view.
Personally, I think
the best form of birth control is a full knowledge of all the possible consequences of sexual activity. If I were in charge I would make sure young people saw the goriest possible photos of disease symptoms, witnessed a bloody screaming natural childbirth video, took care of an actual baby (preferably one with colic), and were able to state correctly the dollar amounts -- monthly and over a lifetime -- that it takes in their area to pay for sustenance, care, and education of a child.
The ones that would be likely to be persuaded anyway, would be. Some teens you'd literally have to lock up to keep them from having sex, but that would probably catch the rest.