Purpose: In this study, the authors evaluated the effect of frequency compression hearing aids on speech perception ability and the time course and magnitude of acclimatization-related changes. Method: Participants included children ages 11-18 years. Speech perception ability was evaluated over well-controlled baseline, treatment, and withdrawal study phases. Study-worn hearing aids were individually fitted to all participants. The authors evaluated speech perception ability using outcomes of speech detection (/s/ and /S/ sounds), /s-S/ discrimination, and plural and consonant recognition. Results: Indices of change were discussed on a case-by-case basis across all study phases. Significant treatment effects were measured for all cases, on at least one measure, with some listeners displaying significant acclimatization trends following a trial of frequency compression. Conclusion: Findings suggest that frequency compression provided varying outcomes, both in benefit and acclimatization, across listeners. For some, a period of acclimatization was necessary before change could be measured. For others, performance remained stable over the time course under evaluation, suggesting that some but not all children will experience improved speech recognition ability after a period of frequency compression hearing aid use. © American Speech-Language-Hearing Association.