Grammatical morpheme production in 4-year-old children.

Despite the importance of grammatical morpheme (GM) production for both clinical decision-making and theoretical accounts of child language impairment, evidence concerning developmental expectations for GM use is inadequate. We studied grammatical morpheme production in 15-minute spontaneous language samples from a large (N = 100), sociodemographically diverse group of 4-year-olds. Substantial variability was observed in both the frequency of obligatory contexts (OCs) and in the percentage of correct usage of GMs. For only one morpheme did all 100 samples contain the minimum number of 3 OCs; for only 7 of the 14 GMs was an adequate number of OCs found in at least half of the 100 samples. Although mean percentages of production from samples with 3 or more OCs were high (> 85%), fewer than 25% of participants contributed to the "group" means for 6 of the 14 GMs. Results from the present investigation indicate a need for caution in interpreting information on GM production derived from samples of this nature from children at this age; the validity of using such data to identify deficits in inflectional morphology for either clinical or research purposes appears questionable.