Previous studies found that children’s judgments of syllable-initial /s/ and /∫/ are more related to the vocalic F2 transition and less related to the fricative-noise spectrum than are adults’ judgments [e.g., Nittrouer, J. Phon. 20, 351–382 (1992)]. Such results have led to a model of speech development proposing that children’s weighting of acoustic cues changes as they gain linguistic experience. The present study tested two requisites of that model, namely that the perceptual weighting of acoustic cues must be flexible and cannot simply reflect a listener’s auditory sensitivities. Adults and 3-year olds participated in two tasks: Identification tasks, using synthetic fricative noises and either natural or synthetic vocalic portions; and discrimination tasks, measuring sensitivity to fricative-noise spectrum and F2 transition. Identification tasks showed the same age-related differences found in earlier studies when natural vocalic portions were used, but these age effects were reduced when synthetic vocalic portions were used. Discrimination tasks showed slightly larger difference thresholds for both the fricative noise and the F2 transition for children than for adults, but this age effect could not explain the age effect on the weighting of those cues for identification. It was concluded that the weighting of acoustic cues is flexible both for adults and for children, and that age-related differences in the weighting of the cues to /s/ and /∫/ are not explained by age-related differences in auditory sensitivities. [Work supported by NIH.]