School active travel contributes to young people's physical activity levels, yet the prevalence is low, and declines with age. Based on determinants from the social-ecological model we investigated changes in school travel behaviour over the transition from childhood to adolescence in participants from the baseline and four-year follow-up of the SPEEDY cohort. Descriptive analysis examined how travel behaviours changed and were related to physical activity. Multinomial logistic regression investigated determinants. Some 38% of participants changed travel mode; 66% from active to passive. Passively traveling participants at follow-up showed a decrease in physical activity. Several social-ecological domains were associated with change. Findings suggest multicomponent interventions are required to support active travel in youth.