Religious and conservative groups have long promoted chastity, saying that lessons about birth control send mixed messages suggesting that premarital sex is really OK.
Now, as many as one in three public schools are following their lead, teaching students that sexual abstinence is not just the best way to prevent pregnancy and disease - it's the only way.
Some schools are eliminating any discussion about contraception and safe sex, except to point out their shortcomings, according to new surveys by the Kaiser Family Foundation and the Alan Guttmacher Institute.
"I think it's fair to say there's wide recognition that abstinence is a very important skill that students should learn," said David J. Landry, coauthor of the Guttmacher study. "Unfortunately, there have not been any rigorous studies of abstinence-only programs that have shown a positive effect."
Guttmacher's survey of 825 superintendents found that among those districts with sex-ed policies, 23 percent taught abstinence only. According to the Kaiser survey of high school principals, 34 percent said abstinence was the main message.
Almost all schools promote abstinence, but most opt for "abstinence-plus" programs that discourage sex but include discussions on contraception, the surveys showed.
"Schools see the need for students to get the very clear message about abstinence to avoid mixed signals," said Robert Frederick, principal of Paxon Hollow in Marple Newtown School District.
During Guerra's twice-weekly classes, her message is as clear as a virgin's conscience: Do not have sex until you are married - or you'll regret it.
"Remember, chastity saves your life," cautioned the 30-year-old nurse as she passed around a basket of LifeSavers candies. "Next time you go on a date, grab a bunch of Lifesavers and put them in your pocket" as a reminder, she said.
While Guerra does not mention God, there is a hint of spirituality in her presentation. Students hear that being chaste is a virtue, and that those who aren't will suffer physically, emotionally and socially.
"Our society loves things that are pure," she said, holding up a bottle of spring water to make her point.
These no-sex programs are most prevalent in the South and least common in the Northeast, according to the Guttmacher survey. In 1996, they got a boost with a $250 million bill for abstinence-only programs, enacted as part of welfare reform.
"When I started out in 1993, most of our work was in Christian schools and churches," said Jill Page, director of education for the Urban Family Council, a Cheltenham-based group that also teaches sexual purity.
Last year, three-quarters of its 406 presentations were given in public schools. Though the group tones down its religious message in public schools, the basic theme remains the same, Page said.
"I can't say in a school, 'Pray for God to enable you to live a life of sexual purity and honor God with your body.' It would be great if I could, but in public schools you can't present that as a motivation."
Like the Urban Family Council, the group that runs the program at Paxon Hollow is faith-based. The Family Life Educational Foundation is an Oreland antiabortion group whose board once included Mike McMonagle, a self-professed "pro-life missionary" who has been arrested more than 40 times at abortion protests.
There is no proselytizing at Paxon Hollow, according to Frederick, who likes the program's emphasis on decision-making and resisting peer pressure. The idea is to teach youngsters about values before they're confronted with sexual choices so they don't have to make a "snap decision," the principal said.
Parents, too, approve of the program, with 84 percent of them giving it a favorable review in a survey last year. So far, none have allowed their children to skip the course, though that's an option.
"When they get older and really start seeing what is confronting them in society, then they can bring in the safe-sex end of it," said Gail McLean, whose 13-year-old son, A.J., will take the six-week course this year. "Let's start right now with no."
Because these programs are relatively new, research about their effectiveness has been inconclusive. The Guttmacher Institute's Landry said the courses that have shown the most promise cover abstinence and contraception.
The benefit of even those programs is small: a delay of three to six months in the onset of sexual activity, he said. Frank Furstenberg of the University of Pennsylvania, a nationally acclaimed expert on teen pregnancy, agreed that the research was "not terribly encouraging."
Though there is growing political support for the anti-sex programs, Furstenberg said they don't do much to deter teens from becoming sexually active - in part because society provides mixed messages.
"I would disagree with that then. I think they are effective," Betty Jean Wolfe, who teaches abstinence in both Urban Family Council and Family Life Educational Foundation programs. Surveys conducted before and after the courses, she said, show an increase in students who say they value chastity and plan to abstain from premarital sex.
About half of all American high school students are sexually active, according to a 1997 Youth Risk Behavior study by the Centers for Disease Control. Though U.S. teenage pregnancy rates have declined in recent years, they are still twice as high as in Britain and Canada, and nine times as high as in Japan.
"America continues to be divided and confused about how to manage publicly this issue in a way that's intelligent," Furstenberg said.
Some people worry that the programs rely too heavily on scare tactics.
"They are designed to induce fear, shame and guilt in young people to scare them away from sex," said Debra Haffner, president of the Sexuality Information and Education Council of the United States in New York. "They basically say if you have sex as an adolescent you will not only lose your reputation, parents' respect and grades, but you're probably going to die also."
At Paxon Hollow, Guerra manages to capture the attention of 19 kids who barely understood the mechanics of puberty with a sports analogy.
The subject at hand is how, she says, the HIV virus passes through the "pores" of a condom.
"It's like a golf ball going through a basketball hoop," she said. "Condoms are made to protect against sperm, not the HIV virus," she added, saying that the HIV virus is smaller than the microscopic holes in the latex.
"Why don't they tell you this?" a boy sitting up front asked.
"Because nobody would buy it," she answered.
Or because many authorities - including the Centers for Disease Control in Atlanta - say it is not true. CDC spokeswoman Terry Hammond said it's a common myth that latex condoms contain holes that allow the passage of HIV.
"Latex condoms have proven extremely effective in stopping [the transmission] of HIV," she said.
According to Peter Brandt of the nonprofit National Coalition for Abstinence Education in Colorado Springs, Colo., Guerra's condom lesson "doesn't reflect purely the reality. You have to draw the line between unwarranted fear language and healthy respect for sexually transmitted diseases."
Wolfe, who oversees the Paxon Hollow program, said the information on HIV and condoms was "medically accurate."
She cited two sources: a 1993 letter to a New Jersey newspaper from a chemist saying condoms didn't protect against AIDS, and a 1994 independent research study of various brands of condoms, which detected viral leakage in some brands (but concluded that most were "an excellent viral barrier.")
But condoms do not protect against the papilloma virus, which causes genital warts, Wolfe noted. Nor do they "protect a broken heart," said Guerra, who began teaching abstinence after working as an obstetric nurse in a Washington hospital and seeing "too many young girls get hurt."
Guerra keeps her class fast-paced and fun. She uses props and jokes, and promises a pizza party if everyone does the homework, brings the books and avoids crude remarks. For the first two classes, at least, they comply.
For one lesson, she gives an athletic-looking boy a long piece of tape and tells him to stick it to her arm and yank it off. He does. She tells him to do it again. And again. And again.
The tape, she says, sticks less and hurts less each time.
"That is what happens to a person who goes from sexual relationship to sexual relationship to sexual relationship. Are they able to bond to the third, fourth, fifth person as much as to the first?" she asks, shaking her head no. Nor will that person be able to bond to the person they eventually marry, she said.
To make a point about condoms, she asked the class if they would use an airline that crashed 14 percent of the time - the failure rate of condoms for pregnancy.
It's probably safe to say no one thinks it's OK for 12-, 13-, 14-year-olds to have sex. Certainly not Chris Bezsylko, 31, the students' health and phys-ed teacher, who thinks the abstinence-only message is a good one.
But with - in his estimation - one-quarter of middle-school students already sexually active, that message alone may not be enough.
"I don't know if it's as realistic as it could be," he said, watching his students laughing and jostling each other as they filed out of the room. "I think the more information kids get, the better equipped they are to make decisions."
Kathy Boccella's e-mail address is email@example.com