The goal of this research programme was to evaluate the role of word lexicality in effecting phonological change in children's sound systems. Four children with functional speech sound disorders (SSDs) were enrolled in an across-subjects multiple baseline single-subject design; two were treated using high-frequency real words (RWs) and two were treated using (low-frequency) non-words (NWs). Dependent variables were learning during treatment, generalization of treated and untreated sounds post-treatment and error consistency indices. The oldest child in the NW group demonstrated slightly greater increases in learning during treatment, and both children demonstrated increases in generalization as well as large decreases in sound error variability. In comparison, one child in the RW group demonstrated untreated sound generalization, as well as decreases in sound error variability. These results suggest that NWs may be useful in helping children learn the sound structure of words containing treated sounds. These findings are interpreted within an established connectionist model accounting for phonological and lexical representations.