In the early years of the "Journal of Child Language," there was considerable disagreement about the role of language input or adult-child interaction in children's language acquisition. The view that quantity and quality of input to language-learning children is relevant to their language development has now become widely accepted as a principle guiding advice to parents and the design of early childhood education programs, even if it is not yet uncontested in the field of language development. The focus on variation in the language input to children acquires particular educational relevance when we consider variation in access to academic language--features of language particularly valued in school and related to success in reading and writing. Just as many children benefit from language environments that are intentionally designed to ensure adequate quantity and quality of input, even more probably need explicit instruction in the features of language that characterize its use for academic purposes. [This article was published in "Journal of Child Language," v41 nS1 p117-123 2014.]