Children with speech, language, and communication needs (SLCN) form a highly heterogeneous group, including those with an unexplained delay in language development known as specific language impairment (SLI). There is growing recognition that multiple mechanisms underlie the range of profiles observed in these children. Broadly speaking, both the domain-general executive attentional system known as working memory and domain-specific linguistic processing have been implicated in children with SLI. It has been challenging to tease apart these influences, however, due to the symbiotic relationship between working memory and language learning. For example, working memory limits might constrain the linguistic detail encoded, whereas poor language knowledge would place greater demands on working memory for retaining unfamiliar phonological information. There is growing evidence for separable impairments in these processing resources leading to relative deficits in linguistic or working memory processes in different children. Such findings have important clinical implications for both the assessment and treatment of children with SLCN.