Abstinence-only sex education is the most effective approach to preventing teen pregnancy and STIs.

In the summer of 1996, as part of the welfare reform legislation that President Clinton signed into law, Congress quietly established a funding stream that would reshape American sex education for the next decade. Title V, Section 510 of the Social Security Act created a program dedicated exclusively to abstinence-until-marriage instruction, providing $50 million annually in federal grants contingent on states teaching that sexual activity outside of marriage was harmful to psychological and physical health. It was not presented as an experiment. It was presented as settled truth.

The ideological premises behind Title V had roots in American conservative social movements of the 1970s and 1980s, which had successfully pushed the argument that the sexual revolution had produced measurable social harms, rising divorce rates, out-of-wedlock births, and sexually transmitted infections, and that education reversing those trends had to start by challenging the premise that teen sexuality was inevitable. If teenagers could be persuaded not to have sex at all, neither pregnancy nor infection would occur. The logic seemed irrefutable. The question was whether persuasion worked.

Federal funding grew sharply after 2000. By 2007, the federal government was spending approximately $170 million annually on abstinence-only programming across the country. The curricula it funded taught that condoms frequently failed, that premarital sex caused psychological damage, and that sexual activity outside of marriage was likely to lead to poverty and family breakdown. Some programs, audited by the House Government Reform Committee in 2004 under Representative Henry Waxman, contained demonstrably false medical claims, one stated that HIV could be transmitted through sweat and tears.

The congressional mandate that produced the funding also, eventually, produced the evidence against it. When Title V was reauthorized in 1997, Congress required the Department of Health and Human Services to commission an independent evaluation of the program's effectiveness. That task fell to Mathematica Policy Research, which designed a longitudinal study tracking students in four federally funded programs across Virginia, Florida, Wisconsin, and Mississippi. The researchers surveyed more than 2,000 students, both those enrolled in abstinence-only curricula and matched controls who received no such instruction.

The results, delivered to Congress in April 2007, were unambiguous. Students who participated in the Title V programs were no more likely to abstain from sex than those who did not. They initiated sexual activity at the same mean age, reported the same number of sexual partners, and engaged in unprotected sex at identical rates. Christopher Trenholm and his colleagues at Mathematica noted that while program participants had somewhat stronger knowledge of certain STDs, this knowledge had not translated into behavioral change. The programs had no measurable effect on the behavior they were designed to change.

The Trenholm report did not stand alone. Kathrin Stanger-Hall and David Hall published an analysis in 2011 in PLOS ONE showing that states with more abstinence-only education had significantly higher rates of teen pregnancy and gonorrhea than states with comprehensive sex education curricula. The correlation was consistent across multiple data sets and held after controlling for income, race, and religiosity. Studies of abstinence pledgers found they were no less likely to have sex before marriage, but substantially less likely to use contraception when they did.

The $170 million per year question was not only whether abstinence-only instruction was effective. It was whether, by displacing instruction on contraception and safer sex, it was actively increasing the harms it claimed to prevent. A curriculum that taught that condoms had a 31 percent failure rate for HIV, a figure with no basis in evidence, and that all premarital sex was psychologically devastating was leaving sexually active teenagers with neither accurate information nor tools to protect themselves.

By 2009, the Obama administration had begun redirecting Title V funding toward evidence-based programs. Most states eventually declined the abstinence-only grants rather than comply with the content restrictions. The clinical trial, in effect, had returned its verdict: the central premise of a decade of federal sex education policy was not supported by the evidence the policy itself had commissioned.