To examine age-related physical activity (PA) patterns between- and within-day in elementary school-aged children with autism spectrum disorders (ASD). PA was recorded every 5-s by uniaxial accelerometry in 35 children (grades 1-2, n = 13; grades 3-4, n = 13; grades 5-6, n = 9) for up to five weekdays and two weekend days. Younger children were more active during weekend days compared with weekdays, while the opposite was observed in older children. Age variation also exists in children's PA levels within a weekday, with this effect being most evident during recess and after school. Weekend days and free time within school days seem appropriate targets when promoting PA in older children with ASD. (Contains 1 figure and 5 tables.)