This study uncovered the patterns of moderate-to-vigorous physical activity (MVPA) in normal-weight and overweight/obese children before, during, and after school lessons. ActiTrainer-based MVPA was assessed over 2 school days (with and without a physical education lesson [PEL] in a sample of three hundred thirty-eight 9- to 11-year-old children (50.3 % female; 29.6 % overweight/obese), in the Czech Republic, during spring 2012. MVPA was quantified based on the step count (number), MVPA duration, and MVPA heart-rate response (minutes). No differences in the MVPA based on the time during the school day were confirmed in normal-weight versus overweight/obese girls, whereas normal-weight boys significantly exceed their overweight/obese peers in step count and after-school and daylong MVPA. Active participation in PEL contributes to a significantly higher step count, exercise duration, and MVPA heart-rate response in normal-weight and overweight/obese boys (p < 0.001) and normal-weight (p < 0.001) and overweight/obese (p < 0.04) girls during school time. Moreover, active participation in PEL significantly (p < 0.04) increases the overall daily step count, duration, and MVPA heart-rate response in normal-weight boys and overweight/obese girls. Active exercise during PEL accounted for 16.7 % of the total number of steps, 25.1 % of overall MVPA duration, and 24.1 % of the MVPA heart-rate response in 9- to 11-year-old children. During days with a PEL, a significantly (p < 0.02) higher number of overweight/obese girls and a higher number of normal-weight boys achieved the duration of 60 min/day of MVPA compared with days without a PEL. Conclusion: Adding one PEL or an equivalent amount of MVPA to the daily school routine appears to be a promising strategy to effectively increase daily MVPA, particularly among overweight/obese girls.