Purpose: As a class, fricatives are more "resistant" to consonant-vowel coarticulation than other English sounds. This study investigates the relative coarticulatory resistance of /[voiceless dental fricative], s, [voiceless palato-alveolar fricative]/ in child and adult speech to better understand the acquisition of individuated speech sounds. Method: Ten 5-year-old children, seven 8-year-old children, and nine college-age adults produced [[schwa]FV] sequences in carrier phrases, where F was /[voiceless dental fricative]/, /s/, or /[voiceless palato-alveolar fricative]/ and V was /ae/, /i/, or /u/. In Experiment 1, coarticulation was perceptually indexed: 65 adults predicted the target stressed vowel based on forward-gated audiovisual speech samples for a subset of four speakers from each age group. In Experiment 2, dynamic spectral measures of the /[schwa]FV/ sequences were analyzed using smoothing spline analysis of variance to again test for vowel effects on fricative articulation across age groups. Results: The perceptual results indicated that fricatives blocked vowel-vowel coarticulation across speaker age groups. Contrary to expectation, vowels were most accurately predicted when F was /s/ and not when it was /[voiceless palato-alveolar fricative]/ or /[voiceless dental fricative]/ across age groups. Acoustic results indicated the expected biomechanically motivated /[voiceless palato-alveolar fricative]/ > /s/ > /[voiceless dental fricative]/ coarticulatory resistance hierarchy in adults' speech. By contrast, /[voiceless palato-alveolar fricative]/ > /s/ were similarly influenced by context in 8-year-olds' speech, and the results from 5-year-olds' speech suggested an influence of order of acquisition in that /[voiceless dental fricative]/ was surprisingly resistant to coarticulation. Conclusion: The study results are taken to suggest that a temporal constraint on fricative articulation interacts with biomechanical constraints during development to influence patterns of coarticulation in school-age children's speech.