"Mind the gap" signs on Amtrak trains warn riders to be wary when they step off a train. We should likewise post "mind the gap" warnings in many of America's schools — alerting students, parents and the public to the very real hazard posed by the huge, and growing, reality gap in U.S. sex education.

Just how cavernous is the gap between the scientific evidence and our sex-education policies? Several authoritative studies released this year show compellingly that there is no evidence base to support the massive federal investment in abstinence-only-until-marriage sex-education programs. And yet, Congress wants to authorize a $28 million funding increase for these hard-line programs, on which we have already wasted about $1.5 billion — including $176 million this year alone.

Let's review the evidence: A recent report by the nonpartisan National Campaign to Prevent Teen and Unplanned Pregnancy finds that "[a]t present, there does not exist any strong evidence that any abstinence program delays the initiation of sex, hastens the return to abstinence, or reduces the number of sexual partners." The report concludes that "studies of abstinence programs have not produced sufficient evidence to justify their widespread dissemination." Is it unreasonable to expect, at a minimum, that such programs demonstrate a positive impact before hundreds of millions of our dollars are poured into them?

Also consider the eight-year, congressionally mandated evaluation by Mathematica Policy Research released in April, which shows that abstinence-only programs have no beneficial impact. Students who participated in a range of curricula funded through the federal Title V abstinence-only program were no more likely than non-recipients to delay sexual initiation, to have fewer partners or to use condoms when they did become sexually active. Apparently, that's what a $176 million annual investment in federally funded abstinence-only programs gets you: no positive impact whatsoever.

Recent research conducted by the Guttmacher Institute further exposes the dysfunctional, and at times outright absurd, nature of our government's approach to sex education. Even though we found that 86 percent of the recent decline in U.S. teen-pregnancy rates is the result of improved contraceptive use, the Bush administration and some members of Congress want to increase funding for abstinence-only programs that-if they mention contraception at all-are prohibited from any discussion of its effectiveness and benefits. And never mind that, as our researchers found, premarital sex is near-universal among Americans. Federal abstinence-only programs now promote abstinence not just for young teens, but are encouraged to do so for all unmarried people through age 29.

Instead, it would be more effective and responsible to provide our young people with the skills and information they really need-both to postpone the onset of sex and to be safe once they do become sexually active, which nearly everyone eventually will. This approach is bolstered by an abundance of evidence, including from the National Campaign's just-released report, showing that a substantial majority of comprehensive sex-education programs-which receive no dedicated federal funding-are effective; indeed, many succeed in delaying teens' initiation of sex, reducing their number of sexual partners, and increasing condom or contraceptive use.

Policy-makers at the state level increasingly get it. Thus far, 14 states have opted not to accept federal funds under the rigid Title V abstinence-only program — among them New York, New Jersey and Ohio. Unshackling their students from hard-line ideology and offering them more comprehensive sex-ed programs instead not only is bolstered by a very strong body of evidence, but also is endorsed by the vast majority of Americans.

Just how overwhelming is the public's support for comprehensive sex education? Even a Zogby survey (chock-full of leading and misleading questions) commissioned by the National Abstinence Education Association (NAEA), the lobbying arm of the abstinence-only industry, found that almost 80 percent of parents agree that learning how to use condoms and other contraceptives correctly "is best for [their] child's health and future." Too bad such instruction is expressly forbidden by current federal guidelines for abstinence-only programs on whose behalf the NAEA lobbies.

In short, one would be hard-pressed to find another issue where the thrust of our policies goes so strongly against the evidence-not to mention against the interests of a generation of American youth. However, Congress now has the opportunity to redeem itself following President Bush's successful veto (on grounds that it is too expensive) of the major appropriations bill that included the increase for abstinence-only funding. As it renegotiates the spending bill, Congress should do right by America's taxpayers and youth and stop-or, at the least, scale back-the funding for ineffective abstinence-only programs.

This article was originally published in the November 20 edition of the Philadelphia Inquirer.