Using a randomized controlled effectiveness trial in 14 schools in Washington State, the evaluation measured Project SUCCESS' effects on perceived harm from substance use, resistance self-efficacy, participation in prosocial activities, normative beliefs, positive peer support, peer pressure, and problem behaviors (rebelliousness and violent behavior). The evaluation found that Project SUCCESS successfully changed one substance-use-related attitude (perceived harm)) and demonstrated a trend toward changing a second only for marijuana (normative beliefs), but failed to change many others (resistance self-efficacy, problem behaviors, peer pressure, and participation in pro-social activities). Although Project SUCCESS significantly increased students' perceptions of harm resulting from alcohol and marijuana use, students in the control group reported greater increases in peer support. Such conflicting evidence of the program's effectiveness was also shown in two opposing trends related to students' perceptions of the prevalence and acceptability of substance use. Those in the intervention group reported positive effects for marijuana, but negative effects for alcohol. Although it is possible that Project SUCCESS and the program's evaluation may suffer from a variety of threats to validity, including implementation, program activities, measurement, or theory failure, the simplest explanation is that students in the intervention group did not attend their alternative schools with sufficient frequency (or for a sufficient length of time on the days they did attend) in order to participate fully in the program. Schools were randomly assigned to program participation (n=7) and control (n=7). 2 tables and 86 references