VARIABILITY IN CHILDRENS USE OF GRAMMATICAL MORPHEMES

The authors analyzed 104 language samples, obtained from 42 different normal language learning children at 25, 29, and 35 months of age, for the proportional use of 11 grammatical morphemes: plural -s. possessive 's. progressive -ing, regular and irregular past, and regular and irregular present, as well as the contractible and uncontractible forms of the copula and auxiliary to be. Wide variability was found among the samples in the proportional use of each morpheme, whether the samples were grouped by age or mean length of utterance (MLU). At ages 25 and 29 months, the range of proportional use was over .95 for 9 of the 11 morphemes, and at 35 months, it was .50 or greater for 8. At an MLU level of 2.50-2.99, the range of scores was .90 or greater for 8 of the morphemes, and over .65 for the remaining 3. By MLUs of 4.00 or more, ranges had narrowed but were still .50 or greater for 4 of the morphemes. Rank order of acquisition by MLU level varied somewhat from that previously reported in the literature (e.g., contractible copula was ranked higher and irregular past was ranked lower than has been reported in other studies). Correlations of MLU and morphane use ranged from .11 to .74. with rho > .60 for only 3 and < .35 for 4 morphemes. Comparisons of these data with those reported in the literature on specifically language-impaired (SLI) children indicated that group means were generally lower for SLI children, but that many of the SLI children's scores overlapped with those of the children studied here.