Development of planning in 4- to 10-year-old children: reducing inhibitory demands does not improve performance.

Currently, there are relatively few tasks suitable for testing planned problem solving in children. We presented 4- to 10-year-old children (N=172) with two planning tasks (sequential planning and advance planning) using the paddle-box apparatus, which was originally designed to investigate the planning skills of nonhuman apes. First, we were interested in the development of children's performance in the two tasks and whether the strategies children used to succeed differed among age groups. Performance improved significantly across age groups in both tasks. Strategies for success in the advance planning task differed among age groups, with 4- and 5-year-olds performing more excess actions, and a greater proportion of irrelevant excess actions, than older children. Findings are discussed in relation to the development of performance in tower tasks, which are a commonly used test of planning ability in humans. Second, based on previous findings with apes, we predicted that introducing measures to reduce the inhibitory demands of the advance planning task would improve children's performance. Therefore, in this study we introduced two methodological alterations that have been shown to improve children's performance in other tasks with inhibitory demands: (a) imposing a short delay before a child is allowed to act and (b) replacing reward items with symbolic tokens. Surprisingly, neither of these measures improved the performance of children in any of the age groups, suggesting that, contrary to our prediction, inhibitory control might not be a key performance-limiting factor in the advance planning paddle-box task.