During her 45 years of teaching, Roffman has witnessed the evolution of the nation’s attitude toward sex education and, as her experience at the public school shows, how uneven that education can be.

Perhaps more than any other subject, sex education highlights the country’s fierce loyalty to local control of schools. Twenty-nine states require public schools to stress abstinence if they teach about sex, according to the latest count by the Guttmacher Institute, a think tank based in Washington, D.C., and New York that promotes reproductive rights. Some of the more outrageous abstinence lessons employ troubling metaphors, such as comparing sexually active, unmarried women to an old piece of tape: useless and unable to bond. Only 17 states require sex education to be medically accurate.

Most research has found that sex education for adolescents in the United States has declined in the past 20 years. Like art and music, the subject is typically not included on state standardized exams and, as the saying goes, “what gets tested gets taught.” In the case of sex education, waning fear about the spread of HIV and AIDS among heterosexual youths has contributed to the decline in instruction, says John Santelli, a professor at Columbia’s Mailman School of Public Health.

But some bright spots do exist, says Jennifer Driver, the vice president of policy and strategic partnerships at the Sexuality Information and Education Council of the United States. For example, in some parts of Mississippi and Texas, there has been a shift away from "abstinence only" to "abstinence plus" curricula, with the latter permitting at least some information about contraception.

Roffman remembers her own sex education while growing up in Baltimore as being limited to a short film in fifth grade about periods and puberty. She began working in sex ed in 1971—when access to birth control was rapidly expanding amid the sexual revolution—helping Planned Parenthood train health-care professionals who were setting up family-planning clinics in the region, and doing broader community outreach.

Four years later, she followed her Planned Parenthood supervisor to the progressive Park School, where students often address teachers by their first name and current tuition runs about $30,000 a year. When she arrived that spring, she heard that the senior-class adviser had recently rushed into the upper-school principal’s office, exclaiming that something had to be done before the seniors’ graduation, because “we forgot to talk to them about sex.”

Read: The case for comprehensive sex ed

During the next several years, Roffman not only made sure the school remembered to talk to students about sex but steadily built up the curriculum. At Park, students learn about standard fare like birth control and sexually transmitted diseases but also delve into issues such as the history of abortion rights, changing conceptions of gender roles, and how to build respectful, intimate relationships.