This study examined the effect of variations in hearing-aid frequency response on real-life functional performance of children with severe to profound hearing loss. A cross-over design was used in a double-blind comparison of the NAL prescription with alternatives that produced either a BOOST or a CUT (6 dB/octave from 0.5 to 2 kHz), relative to the NAL response. The functional performance of 30 children (aged 7 months to 16 years) when wearing hearing aids adjusted to each response over two to four weeks was assessed by using parents' and teachers' observations (PEACH and TEACH scales). Intelligibility judgments and self-reports were also obtained from school-aged children. Results indicated that on average, variations in frequency response resulted in differences in functional performance in real life. There were significant correlations between PEACH and TEACH, and also between children's intelligibility judgments and subjective reports from children and their parents and teachers. The findings support the use of the NAL response for initial fitting, and the evaluation of children's amplification needs by a systematic use of parents' and teachers' observations.