Methods: During the school year 2004 –2005, a total of 7,079 students aged 12–14 years from 143 schools in
seven European countries participated in this cluster randomized controlled trial. Schools were randomly
assigned to either control (65 schools, 3,532 students) or to a 12-session standardized program based on the
comprehensive social influence model (78 schools, 3,547 students). Alcohol use and frequency of alcoholrelated
problem behaviors were investigated through a self-completed anonymous questionnaire at baseline
and 18 months thereafter. The association between intervention and changes in alcohol-related outcomes
was expressed as odds ratio (OR), estimated by multilevel regression model.