ASAP-Jr evaluated how different neighbourhoods shape children and youth’s physical activity habits,^1,2 transportation choices,^3,4,5 and ultimately their health. For example, what neighbourhood features encourage young people to be physically active or choose active transportation? What are the barriers to active transport? We capitalized on ‘natural experiments’ and investigated whether travel patterns, street usage, physical activity, and physical fitness are enhanced when municipalities invest in positive ‘micro-scale’ changes to the built environment (e.g., sidewalks, crosswalks, curb bulges, benches, lighting).