Unlike other animals, human children will copy all of an adult's goal-directed actions, including ones that are clearly unnecessary for achieving the demonstrated goal. Here we highlight how social affiliation is key to this species-specific behavior. Preschoolers watched 2 adults retrieve a toy from a novel apparatus. One adult included…

There is considerable disagreement concerning the age of onset and universality of attainment of Piaget's stage of formal operations. This study examines developmental differences in response to brief prompts in the use of a formal operational approach to the solution of two tasks. The subjects were 10 males and 10 females from each of Grades 5,…