Procedures are described for selecting the gain and frequency response of hearing aids for deaf children and for evaluating aided hearing. These include a comparison of aided thresholds with the speech spectrum to determine how much of the frequency range is functional for each child. This provides a basis for deciding whether to select an aid having a "conventional" (C) response, which de-emphasises the low frequencies, or a low frequency (LF) response which provides more low frequency gain, although not necessarily low frequency emphasis. It is concluded that, for optical aid fitting, some children require "C" responses for both ears, others "LF" responses for both ears and others a "C" response for one ear and an "LF" response for the other. These three possibilities are all required sufficiently commonly that exclusive use of any one would inevitably result in relatively ineffective amplification for many deaf children.