This report describes an experimental program developed by the RAND Corporation to prevent or reduce the use of alcohol, cigarettes and marijuana by adolescents. Section 1 introduces Project ALERT and presents major findings and conclusions from a study which assessed the program's effects at several points over a period of 15 months in 30 California and Oregon schools. Section 2 discusses issues in preventing adolescent drug use. Rationale is presented for the focus on alcohol, cigarettes and marijuana. Prevention is discussed as a strategy for combatting adolescent use of drugs with guidelines for developing and introducing programs. The social influence model is introduced, discussed, and compared with both the information and affective models of prevention. Section 3 describes the curriculum, experimental design and evaluation of Project ALERT. Information about obtaining accurate reports of substance use, and how the program works for different risk groups is included. Section 4 describes the levels of drug use in the sample and presents the results of the study. This section specifically looks at where Project ALERT was effective and where it was less effective. Section 5 presents conclusions and their implications for future drug prevention programs. Appendices provide detailed descriptions of Project ALERT sessions, baseline survey items and detailed program results by substance. (98 references) (LLL)