Objectives. To investigate whether weekday-weekend differences in sedentary time (ST) and specific intensities of physical activity exist among children categorised by physical activity levels. Design. Cross-sectional observational study. Methods. Seven-day accelerometer data were obtained from 810 English children (n = 420 girls) aged 10-11 yr. Daily average min•d-1 spent in moderate to vigorous physical activity (MVPA) were calculated for each child. Sex-specific MVPA quartile cut-off values categorised boys and girls separately into four graded groups representing the least (Q1) through to the most active (Q4) children. Sex- and activity quartile-specific multilevel linear regression analyses analyzed differences in ST, light physical activity (LPA), moderate physical activity (MPA), vigorous physical activity (VPA), and MVPA between weekdays and weekends. Results. On weekdays Q2 boys spent longer in LPA (p<0.05), Q1 (p<0.001), Q2 boys (p<0.01) did significantly more MPA, and Q1-Q3 boys accumulated significantly more VPA and MVPA than at weekends. There were no significant differences in weekday and weekend ST or physical activity for Q4 boys. On weekdays Q2 and Q3 girls accumulated more ST (p<0.05), Q1 and Q2 girls did significantly more MPA (p<0.05), and Q1-Q3 girls engaged in more VPA (p<0.05) and more MVPA (p<0.01) than at weekends. Q4 girls’ ST and physical activity varied little between weekdays and weekends. Conclusions. The most active children maintained their ST and physical activity levels at weekends, while among less active peers weekend ST and physical activity at all intensities was lower. Low active children may benefit most from weekend intervention strategies.