Inference making is fundamental to the construction of a coherent mental model of a text. We examined how vocabulary and verbal working memory relate to inference development concurrently and longitudinally in 4-to 9-year-olds. Four hundred and twenty prekindergartners completed oral assessments of inference making, vocabulary breadth, vocabulary depth, and verbal working memory each year until Grade 3. Concurrently, hierarchical regressions revealed that a greater proportion of total variance in inference making was explained by vocabulary and verbal working memory for younger than older children. Vocabulary breadth was a stronger predictor of inference than verbal working memory, but the opposite pattern was found for vocabulary depth and verbal working memory. The longitudinal relations between inference making, vocabulary, and verbal working memory were investigated in two separate cross-lagged models: one with vocabulary breadth and a second with vocabulary depth. Both vocabulary breadth and depth explained subsequent inference making and verbal working memory throughout the early grades. Inference making also predicted subsequent vocabulary depth. The results highlight the critical role of vocabulary knowledge in the development of inference ability both within and across time, the importance of vocabulary in supporting the development of verbal working memory, and the changing dynamics between language and memory in early development. Educational Impact and Implications StatementInference making is essential for successful listening and reading comprehension. This study examined how vocabulary knowledge (breadth: number of words known, and depth: what is known about a word's meaning) and verbal working memory were related to 4-to 9-year-olds' ability to make the inferences necessary to understand spoken narratives. Vocabulary knowledge and verbal working memory were stronger predictors of concurrent inference making ability for younger than for older children. Across time, reciprocal relations were evident: inference making predicted subsequent vocabulary depth, and both aspects of vocabulary knowledge supported later inference making and working memory. Educators should be aware of the critical roles of vocabulary and verbal working memory to young children's inference making, and how good vocabulary skills support verbal memory. Of note are the reciprocal relations that exist between vocabulary and inference; both skills should be fostered in the classroom to mutually support each other.

Educational Impact and Implications StatementDespite improvements in word-level reading instruction, many children continue to struggle with reading comprehension. In this study, we tested a whole-class, supplemental curriculum, Let's Know!, designed to support prekindergarten and kindergarten children's oral language and comprehension skills. We found that Let's Know! improved children's knowledge of vocabulary used in the curriculum and some comprehension-related skills but did not impact scores on standardized language comprehension measures. Results provide evidence that classroom instruction can improve some skills related to later comprehension; however, more work is necessary to develop and validate curricula that directly impact language and reading comprehension.