The present study provides an implementation fidelity, process, and immediate outcomes evaluation of Project Towards No Drug Abuse (TND), a drug prevention program targeting continuation high school youth (n = 1426) at risk for drug abuse. A total of 24 schools participated in three randomized conditions: TND Only, TND and motivational interviewing follow-up, and no treatment control. Fidelity was high: across program schools the curriculum was implemented as intended and was received favorably by students. Relative to controls, intervention conditions produced effects on hypothesized mediators, including greater gains in program related knowledge, greater reductions in drug use intentions, and positive changes in motivation. However, few generalizations to attitudes and intentions regarding risky sexual behavior were found. The pattern of results suggests that the experimental manipulations worked as intended. (Contains 3 tables.)