The aim of this study was to assess how children's personal exposure to fine particulate matter (PM2.5) during the school commute is influenced by mode of travel and neighborhood environment in a mid-sized Canadian city. A total of 101 commutes to and from school were tracked using a GPS, and personal exposure to PM2.5 along commute routes was assessed by spatially-referencing the monitored exposure levels with time-synchronized GPS data. Students who walked to and from school were exposed to lower PM2.5 concentrations than those in cars or riding the school bus. There was also a significant difference in mean PM2.5 concentrations by the built environment, with children who walked to school in suburban neighborhoods experiencing higher personal concentrations than children in urban neighborhoods. To reduce children's daily exposure to air pollutants, neighborhoods should be designed to maximize the number of children who are able to walk between home and school.