Vocabulary size predicts behavioral problems in emotionally reactive children.

Internalizing and externalizing behavioral problems place children at an increased risk for low academic achievement and socioemotional maladjustment. Children's language skills and level of emotional reactivity have been shown to predict behavioral problems later in development. Yet, there is an absence of research investigating vocabulary by negative emotionality interactions with respect to the development of behavioral problems during early childhood. Our study sought to fill this gap by examining whether the relation between preschool (age 3) vocabulary size and internalizing/externalizing problems during the early school years (age 6) is moderated by preschool negative emotional reactivity, even after controlling for preschool behavioral problems as well as children's socioeconomic background. Longitudinal data was collected from 256 typically developing children (129 girls, 75% White) and their mothers (64% held a college degree). Linear regression analyses revealed moderate rank-order stability in children's internalizing and externalizing problems across this period of development. Evidence of an interaction effect emerged in both the internalizing and externalizing problems regression models. That is, age 3 vocabulary was negatively related to age 6 behavioral problems, but only among children exhibiting higher levels of negative emotional reactivity. Our results indicate that early vocabulary acquisition may serve as a buffer against adverse behavioral outcomes in children with a natural propensity toward expressing negative emotions. These findings point to a more nuanced picture of the relations between language, emotional reactivity, and behavioral problems in childhood, which are discussed in greater detail to inform future intervention and educational research.