For many decades, tool use has been viewed primarily as a cognitive achievement, an ability that separates not only adults and older children from infants, but humans from virtually all other species. According to this standard account, tool use and associated means-ends behaviors are dependent on symbolic or representational thinking. Organisms…

A series of Piagetian concrete operations period tasks dealing with classificatory concepts was administered to 280 children (40 subjects from each of seven levels--preschool, kindergarten, and first, second, third, fourth, and sixth grades). Significant main effects for age were found for all the tasks. Few significant sex differences were…