Where's the ball? Two- and three-year-olds reason about unseen events

Children 2, 21/2, and 3 years of age engaged in a search task in which they opened 1 of 4 doors in an occluder to retrieve a ball that had been rolled behind the occluder. The correct door was determined by a partially visibl e wall placed behind the occluder that stopped the motion of the unseen bal l. Only the oldest group of children was able to reliably choose the correc t door. All children were able to retrieve a toy that had been hidden in th e same apparatus if the toy was hidden from the front by opening a door. An alysis of the younger children's errors indicated that they did not search randomly but instead used a variety of strategies. The results are consiste nt with the Piagetian view that the ability to use representations to guide action develops slowly over the first years of life.