Five subtypes of developmental phonological disorders.

Evidence for subgroups among developmental phonological disorders based on etiological origins, as opposed to the alternative linguistic view of childhood phonological disorders as a learning problem of unknown origin, is presented. A three-parameter framework that arranges relevant individual differences (mechanism, cognitive-linguistic, and psychosocial) is proposed for study and classification of the phonological disorders. The disorders are studied in relation to developmental correlates and speech-sound normalization. This permits study of these variables in relation to severity and forms of expression and interaction. Subgroups of "speech delay," each of which reflects phonological consequences, are suggested. Residual articulation errors are classified based on causal origins, possibly influenced by the developmental context in which precise articulation is an acquired skill and differentiated from genetic origins posited for speech delays and those related to specific hearing, motor-speech, and psychosocial origins. Exploration of causal origins provides advantages for both assessment and intervention as well as prevention.