Purpose. This study investigated the longitudinal development of two important contributors to reading comprehension, grammar and vocabulary skills. The primary interest was to examine the trajectories of the two skill areas from preschool to third grade.
Methods. The study involved a longitudinal sample of 420 children from four sites. Language skills including grammar and vocabulary were assessed annually with multiple measures. Multivariate latent growth curve modeling was used to examine the developmental trajectories of grammar and vocabulary, to test the correlation between the two domains, and to investigate the effects of demographic predictors on language growth.
Results. Results showed that both grammar and vocabulary exhibited decelerating growth from preschool to grade 2. In grade 3 grammar growth further flattened while vocabulary continued to grow stably. Growth of vocabulary and grammar were positively correlated. Demographic characteristics such as child gender and family socioeconomic status were found to predict the intercept but not the slope of the growth trajectories.
Conclusions. Children’s growth in grammar skills is differentiated in a number of important ways from their growth in vocabulary skills. Results of this study suggest the need to differentiate these dimensions of language when seeking to closely examine growth from preschool to primary grades.