Class inclusion performance: Effect of intermingling the subsets

Abstract

Many findings in the literature on Piaget's class inclusion task are consistent with the proposal that children's performance on the task improves if their attention is drawn to the superset and/or away from the contrast between the subsets. It would also be consistent with this proposal if intermingling the subsets improved class inclusion performance. Previous studies, however, found no such improvement. It was hypothesized that intermingling the subsets does indeed facilitate performance, and that the contrary findings were obtained because the authors concerned relied exclusively on within‐subjects analyses when comparing performance on class inclusion tasks with separated and intermingled subsets; this approach ignores the dangers posed by order effects that bring performance on similar Piagetian tasks closer together than they would otherwise be. The hypothesis was tested on a sample of 80 children (mean age 7 years 3 months) and was supported. A possible explanation for the order effects that were found is presented and the implications for other types of Piagetian studies are noted.