Two main forms of sex education are taught in American schools: comprehensive and abstinence-only. Comprehensive sex education covers abstinence as a positive choice, but also teaches about contraception use and the avoidance of STIs if the teen becomes sexually active. A 2002 study conducted by the Kaiser Family Foundation found that 58% of secondary school principals describe their sex education curriculum as comprehensive. The difference between these two approaches, and their impact on teen behavior, remains a controversial subject in the United States.