Vocabulary development of Late-Talking children: a longitudinal research from eighteen to thirty months of age

In this study the vocabulary development of 31 children has been longitudinally monitored through monthly administration of the Italian version of the MacArthur Communicative Development Inventory (Caselli & Casadio, 1995), starting from 18 months of age. Data collection ended when children reached a vocabulary size of 500 words or when they were 30 months old. The sample has been selected from a larger group (104 children) on the basis of a vocabulary size, at the starting point, of less than 30 words. Twelve children, which at 24 months of age did not yet reach a vocabulary size of 50 words, constituted the ”Late Talker group” and the characteristics of their vocabulary development will be analysed in comparison with average children data. More specifically, the vocabulary composition of children is analysed distinguishing between: 1) Percentage of common nouns; 2) Percentage of predicates 3) Percentage of grammatical function words; 4) Cumulative percentage of onomatopoeic words, routines and names for people. The analyses verify the existence of qualitative difference in the vocabulary composition, at different stages of vocabulary development, between late talkers and average children.