The main objective of this study was to access slow mapping, the gradual elaboration and reorganization process of word learning that takes place over time, through word definition and word association tasks. We included 96 preschool and kindergarten children from two age groups (3- and 5-year-olds) as well as two SES groups (lower and upper SES) in an effort to examine age trends in knowledge of familiar object labels in children with significantly different vocabulary sizes (as determined by Peabody Picture Vocabulary Test-III). This study served to determine changes that occur in the types of information provided in word definitions and associations that accompany changes in age and vocabulary size. Both age and SES were strongly related to many aspects of children's word defining skill and to some aspects of children's word associations. Differences in vocabulary size, knowledge of proper definitional form, and the gradual elaboration of words, meanings over time (slow mapping) are implicated in both the age and SES effects.