The production of the grammatical morphemes studied by Brown and his colleagues was examined in free speech samples from a cohort of 4-year-olds with a history of slow expressive language development (SELD) and a control group of normal speakers. Results suggest that children with SELD acquire morphemes in an order very similar to that shown in previous acquisition research. Children who were slow to begin talking at age 2 and who continued to evidence delayed expressive language development by age 4 showed mastery of the four earliest acquired grammatical morphemes, as would be expected, based on their MLUs, which fell at Early Stage IV. Four-year-olds with normal language histories produced all but one of the grammatical morphemes with more than 90% accuracy, as would be expected based on their late Stage V MLUs. Children who were slow to acquire expressive language as toddlers, but who "caught up" in terms of sentence length by age 4 did not differ in MLU from their peers with normal language histories. However, they had acquired fewer of the grammatical morphemes. The implications of these findings for understanding the phenomenon of slow expressive language development are discussed.
Paul, Rhea, Alforde, S. "Grammatical Morpheme Acquisition in 4-Year-Olds With Normal, Impaired, and Late-Developing Language." Journal of Speech and Hearing Research 36.6 (1993): 1271-1275.