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Speech samples were taken from 21 children aged 16-40 months covering a wide range of mean utterance length. Presence or absence of 14 grammatical morphemes in linguistic and nonlinguistic obligatory contexts was scored. Order of acquisition of the morphemes was determined using two different criteria. The rank-orderings obtained correlated very highly with a previously determined order of acquisition for three children studied longitudinally. Age did not add to the predictiveness of mean length of utterance alone for grammatical development in terms of which morphemes were correctly used. The approximately invariant order of acquisition for the fourteen morphemes is discussed in terms of three possible determinants of this order. Frequency of use in parental speech showed no correlation with order of acquisition, but grammatical and semantic complexity both correlated highly with acquisition order.

This study examined the comprehension of third person singular /s/ as a number agreement marker in children speaking Mainstream American English (MAE). Sixty-two MAE-speaking children aged 3-6 years were presented with a comprehension task where they had to focus on the verb as a clue to number agreement. Overall, results showed that only the 5- and 6-year olds were sensitive to third person singular /s/ as an index of subject number in comprehension, despite their earlier command in production. The implications for development of agreement are discussed.

Various arguments are reviewed about the claim that language development is critically connected to the development of theory of mind. The different theories of how language could help in this process of development are explored. A brief account is provided of the controversy over the capacities of infants to read others' false beliefs. Then the empirical literature on the steps in theory of mind development is summarized, considering studies on both typically developing and various language-delayed children. Suggestions are made for intervention by speech language pathologists to enhance the child's access to understanding the minds of others.