Objective: To compare physical activity and sedentary time among young children whose schools adhere to traditional (i.e. three outdoor playtimes = 70 minutes) versus balanced day (i.e. two outdoor playtimes = ~55 minutes) schedules in Ontario full-day kindergarten classrooms. Design: The project was part of a larger, 2-year cross-sectional study. Setting: Full-day kindergarten classrooms across London, Ontario, Canada. Methods: Participants included 113 young children (mean age = 4.69 years; standard deviation [SD] = 0.66 years) from eligible full-day kindergarten programmes. Participants' physical activity and sedentary data were collected using Actical accelerometers worn for five consecutive days during school hours only. Type of school schedule and periods of outdoor play were captured using the Environment and Policy Assessment and Observation tool. Results: Participants mean activity rates (i.e. sedentary time, light physical activity, moderate-to-vigorous physical activity [MVPA] and total physical activity [TPA]) during school hours were similar across both formats. Participants' overall daily physical activity and sedentary time did not significantly differ across school schedule type (p > 0.05); however, participants adhering to the traditional schedule accumulated significantly more TPA outdoors than those following the balanced day schedule. Conclusion: Neither schedule format appeared to be superior with regard to supporting overall daily physical activity nor minimising sedentary time in school, although children adhering to the traditional schedule format did accumulate more physical activity during periods of outdoor play. Regardless of schedule type, steps are warranted to encourage additional movement (and minimise sedentary behaviours) in the school setting by school and public health officials.