Background: Despite recommendation and confirmed physical activity benefits, participation in active transportation to school (ATS) has continued to decline. This study’s purpose was to create and test a model of ATS that is directly explained by the constructs of parent attitude, the physical environment, and social capital controlling for age and gender. Methods: Participants were parents (N = 248) of children at 6 elementary and 2 middle schools in 1 district in the Southwestern United States. The survey included previously validated behavior, environmental, attitude, and social items (eg, Safe Routes to School Parent Survey/U.S. General Social Survey). Structural equation modeling was used to test the fit of the model and whether parent attitude, the physical environment, and social capital were associated with active transportation. Results: An adjusted measurement model was a good fit for the data. The physical environment (β = 0.391; P < .01) as well as parent attitude (β = 0.535; P < .001) were positively associated with ATS. Conclusion: This study supports a model of ATS, affirming that parent attitude, the physical environment, and social capital are effective constructs from which to conceptualize associations with walking and biking to school.