Adaptive test procedures were used to estimate: (1) boundaries between perceptual “categories” of a labeling, or identification, task and (2) the just‐discriminable difference to each side of the midpoint of a 13‐item /ba/‐/da/‐/ga/ continuum of 4‐formant, synthesized syllables (AX task). At the locus of the /ba/‐/da/ boundary: (1) both 10‐year olds and adults had significantly better discrimination than 6‐year olds; (2) 10‐year‐olds' categorical boundaries were significantly different from those of 6‐year olds; and (3) only adults showed a significant difference between the discrimination limen and the boundary between “categories.” At the locus of the /da/‐/ga/ boundary, performance of 6‐year‐olds differed significantly from adults'. These results were obtained even though all Ss scored approximately 100% correct on a speech discrimination test—WIPI for children and W‐22 for adults—and parallel results obtained on a monosyllabic word perception task [Elliott, L. L.et al., J. Acoust. Soc. Am.66,12–21 (1979)]. [Supported in part by BEH, NINCDS, and NSF.]