A bill working its way through the Utah legislature would allow schools to drop sex education from their curriculum, as well as forbid any discussion of homosexuality or contraception by teachers.

If the goal is to prevent teen sex, however, Utah lawmakers may be working against their own ends. Research released yesterday by the reproductive health research organization The Guttmacher Institute found that receiving sex education actually delays teen sex.

Of the students in the national survey, 77 percent of women and 78 percent of men who received formal sex education had sex before they turned 20. For young adults with no sexual instruction, those numbers jumped to 86 percent and 88 percent, respectively.

"The problem is that we know the majority of parents do not talk to their teenagers about birth control and many don't even talk to their teenagers about when to have sex," said study author Laura Lindberg, a senior research associate at Guttmacher. "Even when parents do talk to their teens, they can only share what they know, and parents often don't have correct or complete information." [10 Surprising Sex Statistics]

This is not to say that parents don't have a role in sex education, Lindberg told LiveScience. Research has shown that when parents discuss values surrounding sexuality with kids, those values sink in. But teens need medically accurate information about sex, too, Lindberg said.

Utah Bill

Utah House Bill 363 now goes to Gov. Gary Herbert, who has not indicated whether he'll sign it into law. The state Senate passed the bill 19 to 10 on Tuesday (March 6). Supporters argued that schools do not have a role in sex ed.

"I recognize that some parents do not take the opportunity to teach in their own homes, but we as a society should not be teaching or advocating homosexuality or sex outside marriage or different forms of contraceptives for premarital sex," Sen. John Valentine, R-Orem, told the Salt Lake Tribune.

Under current state law, parents may opt their children out of sex education, and districts may choose to teach abstinence-only classes. The new law would allow districts to drop sex ed altogether, and would mandate that only abstinence can be taught.

That means many kids may go without sex education altogether. According to a 2010 National Center for Health Statistics Data Brief, 70 percent of teenage boys and 79 percent of teen girls had talked with their parents about at least one of the following topics: how to say no to sex, methods of birth control, sexually transmitted infections, where to get birth control, how to prevent HIV infection and how to use a condom. But there are clearly gaps in teens' knowledge. For example, according to 2009 research by the National Campaign to Prevent Teen and Unplanned Pregnancy, 41 percent of 18- and 19-year-olds said they knew little or nothing about condoms, and 75 percent knew little or nothing about the pill. By age 19, 70 percent of Americans have had sex.

Parental knowledge

Even when they do talk to their kids about sex, parents may be embarrassed or lack good information on contraception and sexual topics themselves. A 2004 study published in the journal Perspectives on Sexual and Reproductive Health found that parents of teens held misconceptions about both condoms and hormonal birth control.

For example, only 40 percent of parents surveyed believed that condoms are very effective for preventing pregnancy, and only 52 percent thought that the birth control pill could prevent pregnancy most of the time. In fact, condoms prevent pregnancy 97 percent of the time when used correctly, and 86 percent of the time with "typical" use (meaning including the times that people use condoms incorrectly). The pill is 99.9 percent effective with perfect use, and 95 percent effective with typical use. [7 Surprising Facts About the Pill]

Teen-parent relationships are often rife with miscommunication, complicating parental sex ed, Lindberg said. One 2010 study found that parents see other teenagers as promiscuous and sexual, but that they characterized their own children as naïve and immature sexually.

And if parents can't or won't give kids all the information they need, teens turn to peers and the Internet for help, Lindberg said. That can lead them right into a minefield of misinformation. According to a study published in 2010 in the Journal of Adolescent Health, 46 percent of 177 websites commonly frequented by teens contained false information about contraception.

That's why formal sex education is so important, Lindberg said.

"If parents don't know algebra, do we let their children not learn it?" she said.

Sex ed alternatives

For parents who find themselves in the position of having to secure high-quality sex ed for their kids without the help of professional educators, Lindberg recommended thinking of sexual education as a process, not a single sit-down talk.

"It's about developing intimate and caring relationships in one's life," Lindberg said. "So the days of a single talk about the birds and the bees need to be put aside."

The Centers for Disease Control and Prevention is a good online resource for high-quality medical information, Lindberg said. The family physician should be recruited to help talk to teens about sexual health as well.

"Utah legislators can attempt to put their heads in the sand, but the majority of Americans have sex before marriage and have sex before age 20, and they need information on how to be healthy in that behavior," Lindberg said. "Not talking about it does not mean it's not going to happen."

You can follow LiveScience senior writer Stephanie Pappas on Twitter @sipappas. Follow LiveScience for the latest in science news and discoveries on Twitter @livescience and on Facebook.