The application of distinctive feature theory to the analysis of the speech of children with defective articulation is suggested as a clinical approach. Distinctions are made between children with phonetic disorders and children with phonemic disorders. Distinctive feature analyses were made of the articulation test data of a child receiving speech therapy for an articulation disorder at three intervals, at ages 5-2, 5–8, and 6-3. Each analysis was compared with the adult model to reveal the rules of the child’s phonological competence at that time. Each analysis is compared with the preceding one(s) to show the changes in the rule system as the child’s speech gradually approached the adult model. Discussion of these analyses suggests some specific applications of the resulting data to clinical management and some limitations of this approach.