Every few years, parents find new reasons to worry about their teenagers. And while there is no question that some kids continue to experiment with sex and substance abuse, the latest data point to something perhaps more surprising: the current generation is, well, a bit boring when it comes to bad behavior.

By several noteworthy measures, today’s teenagers are growing increasingly conservative. While marijuana use has recently had an uptick, teenagers are smoking far less pot than their parents did at the same age. In 1980, about 60 percent of high-school seniors had tried marijuana and 9 percent smoked it daily. Among seniors today, according to the University of Michigan’s Monitoring the Future survey, which has tracked teenage risk behaviors since 1975, 45.5 percent have tried the drug and 6.6 percent are smoking it frequently.

Adolescent use of alcohol, tobacco and most illegal drugs is also far lower than it was 30 years ago. In 1980, about a third of 12th graders had smoked in the past month; today that number has dropped to fewer than 1 in 5. Teenage alcohol use has reached historic lows. In 1980, 72 percent of high-school seniors said they had recently consumed alcohol, compared with just 40 percent in 2011. In 1981, about 43 percent of 12th graders had tried an illegal drug other than pot; in 2011 that number fell to 25 percent.

Today’s teenagers are also far less likely to have sex or get pregnant compared with their parent’s generation…