This study presents outcomes related to adolescents' alcohol use from an evaluation study testing the effectiveness of The Coalition for Youth Quality of Life Project (Le Regroupement pour la qualité de vie des jeunes). This project is an ecological and participatory approach developed to prevent alcohol and other drug use and misuse among multiethnic youth. The intervention was implemented through four channels of program delivery: families, schools, community organizations, and local government. The study involved 411 sixth graders from eight elementary schools and 380 eighth graders from two junior high schools, in two school districts of the Island of Montreal (province of Quebec, Canada). All students were enrolled in regular classes. Follow-up data were collected 18 months and 30 months after pre-test using a school survey. The findings indicated that the program had no significant impact on alcohol use. The program was, however, capable of producing a significant effect on several hypothesized mediating variables. At first follow-up, the sixth graders showed a higher self-esteem, better peer pressure resistance skills, and a more positive relationship with their father than the controls. The eighth graders were also more inclined to get involved in community activities related to substance abuse prevention and to choose more alternatives to "substance abuse" in their leisure time than the controls. The results are discussed by examining attrition effects and also reasons for program failure. Issues are raised about the evaluation of an ecological and participatory approach.