Abstinence education makes a difference.

In Dr. Jemmott’s research, only about a third of the students who participated in a weekend abstinence-only class started having sex within the next 24 months, compared with about half who were randomly assigned instead to general health information classes, or classes teaching only safer sex. Among those assigned to comprehensive sex-education classes, covering both abstinence and safer sex, about 42 percent began having sex.

Dr. Jemmott’s research followed 662 African-American students at urban middle schools, who were paid $20 a session to attend the classes, plus follow-up and evaluation sessions. The abstinence-only classes covered HIV, abstinence and ways to resist the pressure to have sex.