['Bicycle-related injury remains a major cause of death and injury hospitalization among Australian children. The study aimed to assess the effectiveness of a whole-school intervention to increase the correct wearing of bicycle helmets by primary school children.', 'A randomized intervention trial was conducted in 27 Western Australian primary schools. A major component of the intervention was a peer-led classroom curriculum for 10-12 year old children. Helmet use by cyclists was observed as children were leaving school at baseline (May 2000) and after the first year and second year of the intervention. A cohort of 10-11 year old children in study schools completed a self-administered questionnaire at the same three data collection points.', 'Over the 2 years of the study, observed helmet wearing rates declined by 13% in the control group (from 93% at baseline to 80% at post-test 2) and by 5% in the intervention group (from 89% to 84%) (F = 1.745, p = 0.185). Among the Grade 5/6 cohort students who were regular riders, the likelihood of reporting always wearing a helmet was 1.9 times higher at post-test 1 (z = 2.51, p = 0.012) and 1.7 times higher at post-test 2 (z = 2.13, p = 0.033) for the intervention group than the control group students who did not always wear a helmet at baseline.'] Do evaluation of a school-based peer leader bicycle helmet intervention?