The speech of 7 children with phonological disorders (4 who failed to produce an initial voicing contrast for stops and 3 who failed to produce the alveolar-velar stop contrast) was analyzed for imperceptible acoustic distinctions for seemingly homophonous word pairs. Subjects were audio/video recorded before and during treatment as they produced minimal pairs containing their error and correct sounds. Acoustic measures were VOT and CV locus equations. The presence of acoustic distinctions was taken as evidence for productive knowledge of the sound contrasts. Treatment was applied experimentally and progress was related to pretreatment productive knowledge inferred from acoustic distinctions. A shorter treatment period was observed for subjects attributed to have productive knowledge of the contrast being trained, as compared with those who had no knowledge. One of the 4 subjects with initial voicing errors produced an acoustic distinction between voiced and voiceless stops and required the shortest treatment period to establish the voicing contrast. Two of 3 subjects with velar fronting displayed coarticulatory characteristics of velars and required fewer treatment sessions in comparison with the subject with no such characteristics. Results are discussed in reference to other linguistic and nonlinguistic variables from which to predict treatment outcomes.