Self-regulation has been identified as an area of difficulty for those with mental retardation. The Goodman Lock Box provides measures of two critical aspects of self-regulation—planfulness and maintenance of goal-directed behavior. In this study, the Lock Box performance of 25 children with Down syndrome was compared with that of 43 typically developing children, matched for mental age (24–36 months). Children in both groups showed similar levels of competence, planfulness and distractibility. However, children with Down syndrome displayed more task-avoidant behavior. Some issues related to the measurements obtained from the Lock Box are raised.