Wednesday's news that teen birthrates rates rose in the US for the second consecutive year has set off a fresh round of arguments about federally funded abstinence-only programmes.

Predictably, the pro-abstinence camp considers the statistics evidence that their approach is more essential now than ever. Valerie Huber of the National Abstinence Education Association told the Washington Post: "This is certainly not the time to remove any strategy that is going to provide skills for teens to avoid sex." Retorted Texan-chastity-pledge-devotee-turned-sex-ed-youth-advocate Shelby Knox, reached by email: "If you spend $1.5bn to spew shame-filled garbage to young people and then pass laws that limit their access to good information, contraception, emergency contraception and abortion, then you shouldn't be surprised when the health outcomes aren't to your liking."

As the Post's article notes, this debate is bound to be particularly intense right now, just a few weeks short of when President Barack Obama is expected to announce whether or not he will seek to continue funding abstinence-only programmes.

The evidence has certainly been mounting for those who consider abstinence-only a massive, expensive failure. After a decade and 1.5 billion federal dollars spent promoting abstinence-only, a rigorous scientific study authorised by Congress reported no real difference in when programme participants first had sex, or whether they had sex before marriage, or in their number of sexual partners.

Obama has been a vocal supporter of comprehensive sexuality programmes that stress abstinence but also provide medically accurate information about contraception and how to use it. (Under current restrictions, recipients of federal abstinence-only money are prohibited from teaching about condoms or other contraceptives, other than to discuss failure rates.)

But there are further questions to be asked of yesterday's numbers. Compiled from birth certificate statistics, all they really show is an increase in birthrates among young women. They don't tell us the pregnancy rates, or whether or not the pregnancies were intended, or what (if any) information these women had ever received about contraception.

Former Broadsheet contributor Carol Lloyd, no supporter of abstinence-only, was understandably sceptical about attributing blame solely to those programmes back in December 2007, when the Centres for Disease Control and Prevention reported that teen birthrates had risen for the first time in 14 years. Me too, regarding this most recent set of stats. Why, if the abstinence-only programmes of the past decade are the culprits, has it taken 14 years for the decline in teen pregnancy to reverse itself?

"It takes a while for change to kick in and for a trend to reverse itself," said Dr John Santelli of Columbia University, who studies teenage sexual behaviour and appeared alongside Knox to offer testimony at the congressional hearings on abstinence-only programmes in April 2008. "But there is strong evidence linking HIV education, change in teen sexual behaviours and the declines in teen pregnancy between 1991 and 2004."

Santelli reminded me that the 14-year drop in teen pregnancy followed Everett Koop's tenure as surgeon general (1982-1989). Koop's promotion of HIV education during the years immediately following the first reported cases of the virus in 1981 had real impact among teens: they reported a big upswing in condom use and fewer sexual partners. Then, between 1995 and 2000 (the Clinton years), HIV education dropped while abstinence-only programmes, which discredit condom use while preaching chastity, came into vogue.

And voila. "Now recent behavioural data from the Youth Risk Behaviour Surveys from 2003-2007 suggests declines in teen condom and contraceptive behaviour and little change in sexual activity," said Santelli. "Those data are consistent with the shift to abstinence-only approaches."

Evidence suggests that comprehensive sexuality education works. (Though I don't love the idea of mixing accurate medical information with a lot of value-laden lecturing about the importance of abstinence, and suspect that many teens share my view.) And certainly the abstinence-only camp hasn't produced any compelling evidence to support the foolish and callous notion that keeping teens sexually ignorant will prevent them being sexually active. Time for a change.

This article originally appeared in Salon.com.