BACKGROUND: routes of phonological acquisition in children treated with favorable environments in contrast with unfavorable and neutral environments for production of /z/, and in phonological therapy. PROCEDURES: six children with phonological disorder aged between 4:7 and 7:8 were selected to take part in the study. They were properly authorized by their parents. There were speech-language and complementary evaluations in order to diagnose the phonological disorder. The subjects were matched according to the severity of the phonological disorder, gender, age and aspects of the phonological system in relation to the altered phonemes. Half of the children were treated with words in which the phonemes /z/, and were in favorable environments and the other half with unfavorable and neutral environments. There were eight sessions and, after that, new evaluations were made in order to describe and qualitatively compare the routes of phonological acquisition in the said subjects through the Implicational Model of Features Complexity. RESULTS: the results indicated a small advantage in the therapeutic evolution of two subjects treated with favorable environments, in relation to their matches. However, children treated with unfavorable and neutral environments obtained more positive results than their matches. CONCLUSION: the favorable environments for production of fricatives /z/, and did not determine the therapeutic success, but positively influenced the phonological evolution in the subjects in the study.