In order to reduce the test time in real ear hearing-aid fitting for children, the validity of applying the average real ear to coupler differences (RECDs) in prefitting procedure using a 2cc coupler measurement system was evaluated by checking whether the majority of people's RECDs might occur within 5 dB of the average RECDs (N = 116) in each test frequency and age group. The percentages of occurrence were around 90% in test subjects' RECDs in saturation sound pressure levels (SSPLs) and around 70% in gain in each important test frequency. Appropriate test frequencies in prefitting are 500, 1000, 1500 and 2000 Hz.