BELOW is a handy chart for abstinence advocates. A study by the Centers for Disease Control and Prevention has found a decided link between celibacy and good grades. Among high school students who earn mostly A’s, 32 percent have had intercourse, compared with 69 percent of their peers with D’s and F’s. And on risk-taking measures like consuming alcohol or using condoms, the better students were also the more cautious.

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The study doesn’t point fingers. “We don’t know whether students get good grades because they’re not engaging in risk behaviors,” says Nancy Brener, a health scientist at the C.D.C., or whether sex is part of a downward spiral. “It could be a little bit of both.”

Another cautionary tale — a new study called “Sex and School: Adolescent Sexual Intercourse and Education,” from sociologists at the University of California, Davis, and the University of Minnesota — concludes that while teenagers who hook up have lower grades and college aspirations, sex within a romantic relationship is generally “academically harmless.” Romance, it seems, prevails: committed lovers and abstainers were​ statistically alike.