Everyone who is physically mature enough to become a parent needs to be made aware of how pregnancies occur, all of the ways in which they can be avoided, the impact that those means may have on preventing STD's, and the consequences of contracting STD's. This can not be the exclusive domain of either the parent, the schools, or religious institutions, but needs to be done in cooperation with all of these groups. Conflicting messages will make it that much easier for facts to be ignored.
Those disseminating the information need to be informed as well. Parents, particularly need to know that while they may believe that their kids are not sexually active, they could easily become so. Parents need to be able to communicate with their children and provide an accepting environment. This is not to say that parents must agree with every choice their child makes, but they need to provide an environment in which a child won't feel that they have to hide the consequences of a choice that their parent considers unacceptable.
These are not all of my thoughts on this matter, nor do I believe that they are an overnight cure or even something that would eliminate the desire in society for abortion over the next 50 years. However, they are the best start that I can come up with.