Objective This paper analyses helmet use before and after implementing Helmets for Kids, a school-based helmet distribution and road safety programme in Cambodia.

Methods Nine intervention schools (with a total of 6721 students) and four control schools (with a total of 3031 students) were selected using purposive sampling to target schools where students were at high risk of road traffic injury. Eligible schools included those where at least 50% of students commute to school on bicycles or motorcycles, were located on a national road (high traffic density), had few or no street signs nearby, were located in an area with a history of crash injuries and were in a province where other Cambodia Helmet Vaccine Initiative activities occur. Programme's effectiveness at each school was measured through preintervention and postintervention roadside helmet observations of students as they arrived or left school. Research assistants conducted observations 1–2 weeks preintervention, 1–2 weeks postintervention, 10–12 weeks postintervention and at the end of the school year (3–4 months postintervention).

Results In intervention schools, observed student helmet use increased from an average of 0.46% at 1–2 weeks preintervention to an average of 87.9% at 1–2 weeks postintervention, 83.5% at 10–12 weeks postintervention and 86.5% at 3–4 months postintervention, coinciding with the end of the school year. Increased helmet use was observed in children commuting on bicycle or motorcycle, which showed similar patterns of helmet use. Helmet use remained between 0.35% and 0.70% in control schools throughout the study period.

Conclusions School-based helmet use programmes that combine helmet provision and road safety education might increase helmet use among children.