Over the past decade, politicians have battled about how to reduce the teen pregnancy rate: safe-sex vs. abstinence-only sex education programs, even as films such as "Juno" and births by famous teens such as Bristol Palin and Jamie Lynn Spears seemed to make adolescent pregnancies more socially acceptable. At the same time, after declining for years, the teen pregnancy rate increased, but the pace at which teens were having babies appeared to stop falling or even inch up. Now, the Obama administration has entered the politically sensitive debate, promising to put scientific evidence before political ideology. A $110 million campaign...