Students who participate in one year of "abstinence-only" sex education classes are significantly more likely than those who don't to take a negative view of teen sex, an interim government report concludes.

The report offers what experts called the first reliable, if early, evidence that controversial abstinence-only programs funded by the federal government are able to change attitudes about sex before marriage.

But researchers stress that they do not yet have evidence showing whether the classes actually lead to any delay or avoidance of sexual activity later on or whether teens who choose to have sex despite the abstinence message use condoms or other contraception.

"We know that there are a lot of youths who expect to abstain and do not, or vice versa," says Rebecca Maynard, one of the study's investigators from the University of Pennsylvania.

Read Web MD's "Abstinence vs. Sex Ed."

The preliminary study looked at three federally funded abstinence-only sex education programs used in middle schools in Florida, Mississippi, and Wisconsin, as well as one elementary school program in Virginia. Researchers surveyed 952 students taking comprehensive sex education classes and 1,358 students who attended abstinence-only education.

The abstinence programs differ in content and message, but all tell students that avoiding sex is the only foolproof way to prevent pregnancy and sexually transmitted diseases. The classes also focus on building youths' self-esteem and improving communication skills but don't instruct students on the use of contraceptives.

Read Web MD's "Where Do Kids Learn About Sex?"

Changes in Attitudes

Overall, students enrolled in abstinence-only classes were 8 percent more likely to take a positive view of abstinence and 7 percent more likely to hold a negative view of teen sex. The differences were confined to two of the four programs, though the report's authors called the results "strong evidence" that the classes had altered student's attitudes about sex after one year.

The programs "result in youths holding or supporting views that were more supportive of teen abstinence and less supportive of teen sex," says Maynard. The study was conducted by Princeton, N.J.-based Mathematica Policy Research and commissioned by the Department of Health and Human Services.

Abstinence-only programs also appeared to convince more students that premarital sex carries potential consequences. But the study found that the classes had little or no additional impact on students' self-esteem or on their ability to talk about sex with their parents.

Forty-seven percent of high school students reported having had sex at least once in 2003, down from 54 percent in 1991, according to the CDC. About 425,500 teenage girls gave birth in 2002, though teenage birth rates dropped sharply from 62 to 43 per 1,000 births since 1991, according to the agency.

"Abstinence education has contributed to this decline," says Bridgit Maher, family and marriage policy analyst with the Family Research Council, a conservative group.

Read Web MD's "APA Calls for Comprehensive Sex Ed Programs."

Attitudes = Behavior?

Abstinence-only programs remain highly controversial among educators and health experts, though such programs have been eligible for federal funding since 1998. Some 900 abstinence-only programs are funded through a federal program called Title V, which spends $50 million per year on them.

The programs are strongly backed by the Bush administration and conservative groups, who argue that educating students about contraception encourages early sexual experimentation.

"Students in these programs are recognizing that abstinence is a positive choice they are making," Michael O'Grady, the assistant secretary for planning and evaluation at the Department of Health and Human Services, told reporters Tuesday.

O'Grady called the report "the most rigorous evaluation of its kind."

The study's results suggest that abstinence-only programs "seem to be moving in the direction that they want them to," Sarah Brown, president of the National Campaign to Prevent Teen Pregnancy, tells WebMD.

The report also found "limited evidence" that abstinence-only classes increased some students' expectations to actually avoid sex until marriage.

But Brown stressed that those attitudes may or may not translate to delaying or avoiding sex later on. "What we've always known is that attitudes don't necessarily match behavior. What people say and what they do is often at great variance," she says.

Researchers say they are now evaluating the same group of students to see if abstinence programs affect the likelihood of engaging in sex or using contraception as children reach 16 years of age.

Read Web MD's "One in Five Young Teens Report Having Tried Oral Sex."

By Todd Zwillich, reviewed by Michael W. Smith, MD

SOURCES: First-year Impacts of Four Title V, Section 510 Abstinence Education Programs, Mathematica Policy Research, Inc., June 14, 2005. Rebecca Maynard, co-principal investigator, University of Pennsylvania. CDC. Michael O'Grady, assistant secretary for planning and evaluation, Department of Health and Human Services. Sarah Brown, president, National Campaign to Prevent Teen Pregnancy. Bridgit Maher, family and marriage policy analyst, Family Research Council.