Examining Early Vocabulary Growth Trajectories in Late Talkers in a Low-Income Longitudinal Sample.

Studies show children in low-income households have heightened risk of developing as late talkers (LTs). Scholars have attributed the cause of these differences to variability in child-directed and observed language input, parenting quality, attendance at childcare facilities, or some combination therein, as briefly reviewed. However, this study focuses on a sample entirely of families experiencing low income to explore differences within this group. This study explores growth trajectories for child vocabulary production from age 8-30 months in a racially-diverse low-income longitudinal sample in the U.S. (n = 199). Using multi-level multiple group models, we explore differences in growth trajectories for LTs and non-LT peers (identified: age 22-30 months) and identify the age at which vocabulary sizes begin to significantly differ, controlling for the effects of child age-at-test, sex, primary home language, and mother's education. Results show distinctly different trajectories, such that: (1) LTs experience relatively flat growth resulting in significantly smaller vocabulary sizes over time and (2) divergence occurs at ∼11 months. Future research is needed to fully understand how and why LT trajectories begin to differ so significantly at this age, and how we can better intervene earlier to reduce the likelihood of LT.