The non-word repetition test has been regularly used to examine children’s vocabulary acquisition, and yet there is no clear explanation of all of the effects seen in non-word repetition. This paper presents a study of 25 5-6 year-old children’s repetition performance on three non-word repetition tests that vary in the degree of their lexicality. EPAM-VOC, a model of children’s vocabulary acquisition, is then presented that captures the children’s performance in all three repetition tests. The model represents a clear explanation of how working memory and long-term linguistic knowledge interact in a way that is able to simulate performance in non-word repetition.