The development of the meaning of common nouns may continue well past the early years of language acquisition (Ameel, Malt, & Storms, 2008; Ameel, Malt, & Storms, 2011; Andersen, 1975). The nature of this development is investigated through the application of a formal model to categorization decisions by children aged 7-13 years and adults. Children up till the age of 13 overextend categories. It is established that these overextensions are not due to differences in the manner in which children and adults organize items with respect to the target categories. Even the youngest children appear to know about the internal category organization that informs categorization. Rather, the overextensions are the results of children imposing too tolerant a criterion for category membership on this organization. With age children learn of this discrepancy and gradually reduce it to converge upon the conventional adult meaning.