The Iowa Articulation Norms Project and its Nebraska replication.

The purpose of the Iowa Articulation Norms Project and its Nebraska replication was to provide normative information about speech sound acquisition in these two states. An assessment instrument consisting of photographs and a checklist form for narrow phonetic transcription was administered by school-based speech-language pathologists to stratified samples of children in the age range 3-9 years. The resulting data were not influenced by the demographic variables of population density (rural/urban), SES (based on parental education), or state of residence (Iowa/Nebraska); however, sex of the child exerted a significant influence in some of the preschool age groups. The criteria used to determine acceptability of a production appeared to influence outcomes for some speech sounds. Acquisition curves were plotted for individual phoneme targets or groups of targets. These curves were used to develop recommended ages of acquisition for the tested speech sounds, with recommendations based generally on a 90% level of acquisition. Special considerations were required for the phonemes /ng s z/.