Over 90% of adolescents in Italy gamble. Gambling prevention programs often target adolescents directly. However, training teachers about gambling harms could also help reduce gambling in their students. This study trained one group of teachers about adolescent gambling and provided no training for another group. The researchers compared the gambling and problem gambling behaviours of the students of teachers who either received or did not receive this training. Teachers who received training were more aware of adolescent gambling and gambling-related problems. Their students also showed a decrease in gambling and problem gambling behaviours, and had fewer erroneous beliefs about gambling. Thus, training teachers could be an effective way to reduce gambling in adolescents.