They're doing great, it turns out. Violence, drug use, and sex among teens are down. They like their parents. They're happy. They want to get married and have kids.
How did a whole generation of kids turn out so darn good? Glenn Reynold's says it's because of decentralization!
The question is, why are teens doing better? I think there are two answers. First, people noticed problems, and tried a lot of different approaches. Private organizations, church groups, schools, and—especially—parents started taking a greater role in educating teenagers and encouraging better behavior. As with teen pregnancy, no single policy solved the problem, but multiple approaches tended to make it better until something seen as insoluble just a few years ago began to look, well, solved.
Another—and it's a lesson that policy wonks seem slow to learn—is that people other than policy wonks are capable of learning, and of changing their behavior on their own. Given the chance, and the information, they observe things that work and things that don't, and adjust their lives in ways that seem most likely to get them what they want, if they are allowed to do so. This means that projections of catastrophic future ills are usually wrong, as people learn from experience.
This could be a great new libertarian argument: "We need less government interference—it's for the children's sake!"