PURPOSE: Maturation of the ability to recognize target speech in the presence of a two-talker speech masker extends into early adolescence. This study evaluated whether children benefit from differences in fundamental frequency (f o) contour depth between the target and masker speech, a cue that has been shown to improve recognition in adults. METHOD: Speech stimuli were recorded from talkers using three speaking styles, with f o contour depths that were Flat, Normal, or Exaggerated. Targets were open-set, declarative sentences produced by a female talker, and maskers were two streams of concatenated sentences produced by a second female talker. Listeners were children (ages 5-17 years) and adults (ages 18-24 years) with normal hearing. Each listener was tested in one of the three masker styles paired with all three target styles. Speech recognition thresholds (SRTs) corresponding to 50% correct were estimated by fitting psychometric functions to adaptive track data. RESULTS: For adults, performance did not differ significantly across conditions with matched speaking styles. A mismatch benefit was observed when combining Flat targets with the Exaggerated masker and Exaggerated targets with the Flat masker, and for both Flat and Exaggerated targets paired with the Normal masker. For children, there was a significant effect of age in all conditions. Flat targets in the Flat masker were associated with lower SRTs than the other two matched conditions, and a mismatch benefit was observed for young children only when the target f o contour was less variable than the masker f o contour. CONCLUSIONS: Whereas child-directed speech often has exaggerated pitch contours, young children were better able to recognize speech with less variable f o. Age effects were observed in the benefit of mismatched speaking styles for some conditions, which could be related to differences in baseline SRTs rather than differences in segregation abilities.