Tense Marking in the Kindergarten Population: Testing the Bimodal Distribution Hypothesis.

Purpose The purpose of this study was to explore whether evidence for a bimodal distribution of tense marking, previously documented in clinically referred samples, exists in a population-based sample of kindergarten children from a rural county in Tennessee. Method A measure of tense marking, the Test of Early Grammatical Impairment (TEGI) Screening Test, was individually administered to consented kindergarten students (N = 153) across three elementary schools in a single school district. The consented children constituted 73% of kindergartners in the district. Cluster analysis was used to evaluate the number and composition of latent classes that best fit the distribution of the TEGI Screening Test scores. Results Analysis of the scores revealed a distribution that deviated significantly from normality. Cluster analyses (Ward's, k-means, single linkage) revealed a two-cluster solution as the best fitting model. The very large effect-size difference in mean TEGI Screening Test score between the two clusters (d = 4.77) provides validation of an identifiable boundary delineating typical from atypical tense marking in this sample of kindergartners. The difference in tense marking across the two clusters was not attributable to child chronological age. The percentage of the sample comprising the low-performing cluster aligns with specific language impairment and developmental language disorder prevalence estimates. Conclusion Additional demonstrations of a bimodal distribution of tense marking in future studies with carefully defined samples could strengthen the clinical marker evidence and utility of this linguistic feature.