This study evaluated the relationship between level of program implementation and change in adolescent drug use behavior in the Midwestern Prevention Project (MPP), a school- and community-based program for drug abuse prevention. Trained teachers implemented the program with transition year students. Implementation was measured by teacher self-report and validated by research staff reports. Adolescent drug use was measured by student self-report; an expired air measure of smoking was used to increase the accuracy of self-reported drug use. Regression analyses were used to evaluate adherence; exposure, or amount of implementation; and reinvention. Results showed that all schools assigned to the program condition adhered to the research by implementing the program. Exposure had a significant effect on minimizing the increase in drug use from baseline to one year. Exposure also had a larger magnitude of intervention effect than experimental group assignment. Reinvention did not affect drug use. Results are discussed in terms of research assumptions about quality of program implementation, and possible school-level predictors of implementation