The speech-sound production of severely language-impaired children was monitored in a longitudinal study. In order to generalize findings, acoustical, phonemic, and clinical observation data were collected from thirty children. Results showed that speech-sound acquisition goes through a hierarchical sequence of development and that speech-sound production will deteriorate in a predictable manner depending on the pathology. The authors hypothesize a speech-sound acquisition model (SSAM) based on the development observed.