The immediate goal of sensory assistance is to provide as much sensory evidence as possible about the sound patterns of speech. To determine how well this goal has been met calls for tests that are sensitive to sensory capacity and insensitive to linguistic and cognitive status. At the same time, the results should have predictive validity in terms of the potential for developing speech perception skills. This paper describes data obtained from paediatric hearing aid and cochlear implant users by means of an imitative test of phonetic contrast perception (IMSPAC). It is shown that the primary predictor of IMSPAC performance for aided subjects is degree of hearing loss, with little or no influence of age and communication mode. The primary predictors for Nucleus implantees, however, are communication mode and duration of use. The distribution of scores in the implant group is similar to that of hearing aid users with hearing losses in the 90 to 99 dB range. The more successful implantees (mostly, but not only, orally trained) perform like hearing aid users with hearing losses in the 70 to 89 dB range. The hearing aid data suggest that the IMSPAC test is effective in measuring auditory sensory capacity without confounding by linguistic status. If this is true, the implant data must be interpreted as evidence of the development of auditory perceptual skills during the post-implant period. This interpretation carries important implications for issues of cortical plasticity, acclimatization, the management of childhood deafness, and the evaluation of sensory aid efficacy.