Sex education has long occupied an ideological fault line in American life. Religious conservatives worry that teaching teenagers about birth control will encourage premarital sex. Liberals argue that failing to teach about it ensures more unwanted pregnancies and sexually transmitted diseases. So it was a welcome development when, a few years ago, Congress began to shift funding for sex education to focus on evidence-based outcomes, letting effectiveness determine which programs would get money.

But a recent move by the Trump administration seems set to undo this progress.

Federal support for abstinence-until-marriage programs had increased sharply under the administration of George W. Bush, and focus on it continued at a state and local level after he left office. From 2000 until 2014, the percentage of schools that required education in human sexuality fell to 48 percent from 67 percent. By 2014, half of middle schools and more than three-quarters of high schools were focusing on abstinence. Only a quarter of middle schools and three-fifths of high schools taught about birth control. In 1995, 81 percent of boys and 87 percent of girls reported learning of birth control in school.

Sex education focused on an abstinence-only approach fails in a number of ways.

First, it’s increasingly impractical. Trying to persuade people to remain abstinent until they are married is only getting harder because of social trends. The median age of Americans when they first have sex in the United States is now just under 18 years for women and just over 18 years for men. The median age of first marriage is much higher, at 26.5 years for women and 29.8 for men. This gap has increased significantly over time, and with it the prevalence of premarital sex.

Second, the evidence isn’t there that abstinence-only education affects outcomes. In 2007, a number of studies reviewed the efficacy of sexual education. The first was a systematic review conducted by the National Campaign to Prevent Teen and Unplanned Pregnancy. It found no good evidence to support the idea that such programs delayed the age of first sexual intercourse or reduced the number of partners an adolescent might have.