Project Northland was a randomized trial to reduce alcohol use among adolescents in 24 school districts in northeastern Minnesota. Phase 1 (1991-1994), when the targeted cohort was in grades 6-8, included school curricula, parent involvement, peer leadership and community task forces. The Interim Phase (1994-1996) involved minimal intervention. Phase 2 (1996-1998), when the cohort was in grades 11 and 12, included a classroom curriculum, parent education, print media, youth development and community organizing. Outcomes of these interventions were assessed by annual student surveys from 1991 to 1998, alcohol purchase attempts by young-looking buyers in 1991, 1994 and 1998, and parent telephone surveys in 1996 and 1998. Growth curve analysis was used to examine the student survey data over time. Project Northland was most successful when the students were young adolescents. The lack of intervention in the Interim Phase when the students were in grades 9 and 10 had a significant and negative impact on alcohol use. The intervention used with the high school students as those in grades 11 and 12 made a positive impact on their tendency to use alcohol use, binge drinking and ability to obtain alcohol. There was no impact in Phase 2 on other student-level behavioral and psychosocial factors. Developmentally appropriate, multi-component, community-wide programs throughout adolescence appear to be needed to reduce alcohol use.