Mastery motivation of children with Down syndrome and MA-matched typically developing children was examined. The two groups performed similarly with respect to the quality of their play but differed in level of task engagement and causality pleasure. The children with Down syndrome appeared to be less engaged in the task than were the typically developing group as indicated by shorter sequences of goal-directed behavior and higher rates of toy rejection. In addition, the children with Down syndrome displayed less causality pleasure with object exploration than did the typically developing children.