PURPOSE: to check the effects of phonological therapy using the Modified Cycles Model, and to compare the evolution of two groups of children with phonological disorder, one in which target-words with favorable phonological contexts were used in the treatment, and another one in which unfavorable and neutral contexts were used, in the acquisition of the fricatives /z/, /∫/ and /ℑ/. METHOD: the subjects were six children with phonological disorder aged between 4:7 and 7:8 year old, authorized to take part in the research. They were evaluated in speech-language and complementary exams in order to diagnose the phonological disorder. Half of the children were treated with words where the phonemes /z/, /∫/ and /ℑ/ were in favorable environments and the other half with the phonemes in unfavorable and neutral environments. There were eight sessions and, after that, a new speech evaluation was performed. The following variables were analyzed: changes in the phonological system and in the percentage of consonants correct-revised. Wilcoxon Test (p<0.05) was applied for analyzing the data. RESULTS: the therapeutic evolution was statistically significant for all the subjects in most variables, but there was no statistically significant difference in the comparison among the groups favorable and unfavorable and neutral. CONCLUSION: the therapy showed improvements in the phonological systems for all subjects, but the use of target-words with favorable phonological environments does not determine a better therapeutic evolution.