From objects to quantities: developments in preschool children's judgments about aggregate amount

The impact of object boundaries on children's developing quantitative reasoning was examined in a study of children's judgments about aggregate amount. Children at ages 3, 4, and 5 years were asked to help a Cookie Monster get as much to eat as possible by choosing between alternative collections that differed in the number and size of the cookies they contained and also in aggregate amount. Results indicated that children were heavily influenced by the size of individual cookies at 3 years of age but were generally unsuccessful in aggregating size information across multiple cookies until 5 years. The contrast between children's sensitivity to object sizes from an early age and the relatively late achievement of accurate judgments of aggregate amount underscores the significance for quantitative development of the distinction between discrete objects and mathematical quantities.