Children's vocabulary growth in English and Spanish across early development and associations with school readiness skills.

In line with evidence that variation in children's vocabulary size facilitates learning, we asked whether growth in Mexican and Dominican children's expressive vocabularies in English and/or Spanish would predict later cognitive skills. Children and mothers were video-recorded sharing wordless books at 2, 3, 4, and 5 years, and children were assessed on language, literacy, and math skills at 5 years. Growth in children's English and Spanish vocabularies, based on transcriptions of booksharing interactions, predicted specific cognitive skills and was associated with changes to mothers' language use across time. Mothers' years in the United States predicted children's English vocabulary growth.