Until recently, the challenges inherent in measuring comprehension have impeded our ability to predict the course of language acquisition. The present research reports on a longitudinal assessment of the convergent and predictive validity of the CDI: Words and Gestures and the Computerized Comprehension Task (CCT). The CDI: WG and the CCT evinced good convergent validity however the CCT better predicted subsequent parent reports of language production. Language sample data in the third year confirm this finding: the CCT accounted for 24% of the variance in unique word use. These studies provide evidence for the utility of a behavior-based approach to predicting the course of language acquisition into production.

This longitudinal assessment concentrated on the relation between the Home Literacy Environment (HLE) and early language acquisition during infancy and toddlerhood. In Study 1, after controlling for SES, a broadly-defined HLE predicted language comprehension in 50 infants. In Study 2, 27 children and their primary caregivers returned for further analyses. Findings revealed that the HLE measured in infancy predicted language production in toddlerhood, and maternal redirecting behaviors measured in toddlerhood were negatively associated with expressive language. Results across both studies indicate the importance of a broadly-defined HLE (including joint attention and parent-child conversation) for language development. Taken together, these findings highlight the importance of the HLE in supporting both receptive and expressive vocabulary growth in the second and third years of life.