"Working memory" is a term used to refer to the systems responsible for the temporary storage of information during the performance of cognitive tasks. The efficiency of working memory skills in children may place limitations on the learning and performance of educationally important skills such as reading, language comprehension and arithmetic. Originally published in 1992, this monograph considers the development of working memory skills in children with severe learning difficulties. These children have marked difficulties with a wide range of cognitive tasks. The studies reported show that they also experience profound difficulties in verbal working memory tasks. These memory problems are associated with a failure to rehearse information within an articulatory loop. Training the children to rehearse material is shown to help alleviate these problems. The implications of these studies for understanding normal memory development, and for models of the structure of working memory and its development are discussed. It is argued that the working memory deficits seen in people with severe learning difficulties may contribute to their difficulties on other cognitive tasks.