Background: School environments providing a wide selection of physical activities and sufficient facilities are both essential and formative to ensure young people adopt active lifestyles. We describe the association between school opportunities for physical activity and socioeconomic factors measured by low-income cutoff index, school size (number of students), and neighborhood population density. Methods: A cross-sectional survey using a 2-stage stratified sampling method built a representative sample of 143 French-speaking public schools in Quebec, Canada. Self-administered questionnaires collected data describing the physical activities offered and schools' sports facilities. Descriptive and bivariate analyses were performed separately for primary and secondary schools. Results: In primary schools, school size was positively associated with more intramural and extracurricular activities, more diverse interior facilities, and activities promoting active transportation. Low-income primary schools were more likely to offer a single gym. Low-income secondary schools offered lower diversity of intramural activities and fewer exterior sporting facilities. High-income secondary schools with a large school size provided a greater number of opportunities, larger infrastructures, and a wider selection of physical activities than smaller low-income schools. Conclusions: Results reveal an overall positive association between school availability of physical and sport activity and socioeconomic factors.