From Terrible Twos to Sassy Sixes: The Development of Vocabulary and Executive Functioning Across Early Childhood

Early childhood marks a time when word learning is accompanied by rapid growth in the cognitive processes that underlie self-modulated and goal-directed behavior (i.e., executive functions (EF)). Although there is empirical evidence to support the association between EF and vocabulary development in childhood, inconsistent findings have been reported regarding the extent to which early EF abilities predict later vocabulary outcomes and vice versa. Thus, the first aim of the present study was to employ a stringent analytic approach to examining the longitudinal relations between EF and vocabulary across multiple waves in early childhood (i.e., at ages 2, 3, 4, and 6). Among the studies that have documented a link between children's early and later EF/vocabulary skills, the underlying mechanism(s) that can account for this association have yet to be identified. As such, the second and third aims of this study were to investigate children's private speech and visual attention skills as potential mediators of the hypothesized link between early and later EF/vocabulary. The results indicate that after controlling for maternal education, a unidirectional cross-lagged panel model best fit the data. That is, across all measurement waves, children's vocabulary scores at one timepoint were positively predictive of their EF performance at the following timepoint. Although no evidence of mediation was detected, a significant and novel association emerged between children's early vocabulary scores and their later private speech production. Moreover, this study was able to replicate the well-established link between visual attention and receptive vocabulary among a sample of older children.