A group randomized controlled trial tested the efficacy of the Friendly Schools program to reduce student bullying behaviour. This socio-ecological intervention targeted the whole school, classroom, family, and individual students to reduce bullying behaviour. Self-report data were collected in 29 schools over three years from a cohort of 1968 eight to nine-year-olds. Surveys measured frequency of being bullied, bullying others, telling if bullied and observing bullying. Results indicate that intervention students were significantly less likely to observe bullying at 12, 24 and 36 months and be bullied after 12 and 36 months, and significantly more likely to tell if bullied after 12 months than comparison students. No differences were found for self-reported perpetration of bullying. The findings suggest whole-of-school programs that engage students in their different social contexts appear to reduce their experiences of being bullied and increase their likelihood of telling someone if they are bullied.