School-based health clinics, adolescent pregnancy prevention programs offering comprehensive health services, represent the latest initiative to reduce the incidence of teenage pregnancy. Researchers at Johns Hopkins University designed and administered a pregnancy prevention program which offered sexuality education and family planning services to black junior and senior high school students in two Baltimore, Maryland public schools. Students received nearly three years of sexuality education, free medical and contraceptive services, pregnancy testing, and contraception counseling. The attitudes, knowledge, and sexual practices of these students were compared with those of a control group of students in two other Baltimore secondary schools with no school-based family planning services. Control subjects completed self-administered questionnaires at the beginning and end of the evaluation; experimental subjects completed questionnaires four times during the evaluation period. The results revealed that, compared to control school students, students in the experimental schools displayed a greater knowledge of sexuality and a greater tendency to use effective contraception. The pregnancy rate among experimental high school students decreased 30.1% while the control high school students' rate increased 57.6% over the same 56-month period. Unfortunately, a weakness in the study design, combined with the failure to control for and/or properly quantify key variables, limits the study's usefulness to the academic and policy making communities. (NB)