This report investigates perceptual functioning in the kindergarten first-grade period for slow- and average-maturing children. Two sets of auditory and visual tasks were devised: (1) identifying the first of an ordered pair of lights or tones when speed of presentation was a factor, and (2) categorizing each stimulus signal either by a uni- or dual response. Consistent patterns of behavior were found for each group of children when reading readiness scores, grade level, and sensory modality were the crucial variables. Deficiencies in auditory, but not visual, perceptual encoding were found in slow learners' first-grade performance. (Author)