A nationwide study of six school-based clinics (SBCs) reviews factors contributing to the development of the SBC movement and gives recommendations to enhance clinic effectiveness. Clinic utilization and its impact on medical care, on students' risk-taking behaviors, and on pregnancy prevention are also assessed. Student populations in schools with clinics are compared to student populations in schools without clinics. Data were obtained from interviews with students and school and clinic staff, client records, the Student Health Survey, and longitudinal birthrate records. Findings indicate that SBCs successfully provide students with regular comprehensive health care. Whether SBCs actually increase student access to medical care or simply replace former providers remains a question. SBCs show potential for the reduction of students' alcohol and tobacco use, but appear to have no effect on pregnancy rates. Contraceptive use among sexually active teens increases when SBCs provide both access and information. With adequate financial and community support, SBCs may improve health care and reduce risk-taking behavior among students. (28 references) (LMI)