Grammatical morphology and the lexicon in children with specific language impairment.

We examined the use of grammatical morphology by preschool-age English-speaking children with specific language impairment (SLI) as a function of their lexical diversity. Relative to a group of normally developing (ND) preschoolers, these children's use of finite-verb morphology logged behind expectations based on the number of different verbs they used. Noun-related morphology fell below expectations based on overall lexical diversity. Differences between the ND children and children with SLI were also seen for the slope of the increases in finite-verb morphology as a function of lexical diversity, with shallower slopes in the SLI data. The findings of this study add to existing evidence suggesting that a measure of finite grammatical-morphology use has promise as a clinical marker of SLI in English.