Dynamic assessments (DA) of language have been shown to be a useful addition to the battery of tests used to diagnose language impairments in children, and to evaluate their skills. The current article explores the value of the information gained from a DA in planning intervention for a child with language impairment. A single case study was used to demonstrate the detailed qualitative information that can be derived from a DA procedure, and how that information may be used to elicit greater gains from intervention. The participant was a boy, aged 9, with a previously diagnosed language impairment. He was receiving language therapy regularly in a language resource base attached to his school. The CELF-3(UK) was used to monitor changes in his language, before and after two periods of intervention. The initial baseline phase consisted of regular ongoing language therapy. The second phase of therapy was modified by the speech and language therapist after receiving a report of the child’s performance on the Dynamic Assessment of Sentence Structure (DASS; Hasson et al., 2012), and observations of the child’s metalinguistic and metacognitive awareness. Greater gains observed in the second phase of therapy reflected the good modifiability shown by the child’s performance on the DASS.