Adults with autism spectrum disorders (ASD) have shown deficits in switching between rules governing their behaviour, as have high-functioning children with ASD. However, there are few studies of flexibility in lower-functioning children with ASD. The current study investigated this phenomenon with a group of low-functioning children with ASD compared to a mental-age-matched comparison group. The ASD group learned an initial discrimination task as quickly as the matched comparison group, but when the rule governing the discrimination was shifted, the comparison group learned the task with fewer errors, and made the discrimination more quickly than the groups with ASD. These findings suggest that low-functioning children with ASD do display the predicted deficits in extra-dimensional shift. (Contains 1 table and 2 figures.)