Purpose: This article considers how the language performance of school-age children with language impairments, such as developmental language disorder, is influenced by the reciprocal relationship of existing linguistic knowledge and working memory resources and the resultant implications for assessment. Method: A viewpoint is provided by reviewing working memory theory, empirical evidence of the reciprocal relationship between working memory and existing language knowledge, and critically evaluating available standardized and nonstandardized tools designed to assess working memory or linguistic skills. Conclusions: Speech-language pathologists with an excellent understanding of the reciprocal relationship between working memory and linguistic knowledge will need to examine performance across tasks and contexts varying in these demands in order to achieve an accurate clinical profile of relevant strengths and weaknesses for individual children.