The role of hearing, although invisible, is critical to the development of language and literacy skills across key stage 1. Yet, Foundation stage and key stage 1 pupils are the most likely of all children to experience reduced hearing sensitivity, under developed listening skills and a less than ideal acoustic learning environment. The paper examines the potential impact of each of these three factors on the effectiveness of classroom teaching. First, we consider why young children may not always hear or recognize differences in the phonological (phonemic) components of speech sounds that are so fundamental to the development of listening skills, spoken language and reading. Second, the effect of everyday classroom activities on the acoustics of the speech signal and how this relates to children's learning is discussed. Third, the listening and speech skills that one might expect a child to have acquired by and during key stage 1 are explored. Only when these three factors are known, understood and effectively developed, will teachers achieve the most from their spoken contributions in the classroom. (Contains 4 figures and 3 tables.)