Purpose: Accurate production of lexical stress within English polysyllabic words is critical for intelligibility and is affected in many speech-language disorders. However, models of speech production remain underspecified with regard to lexical stress. In this study, the authors report a large-scale acoustic investigation of lexical stress production in typically developing Australian English-speaking children ages 3-7 years (n = 73) compared with young adults (n = 24). Method: Participants named pictures of highly familiar strong-weak and weak-strong polysyllabic words. Of 388 productions, 325 met criteria for acoustic measurement. Relative vowel duration, peak intensity, and peak f[subscript 0] over the first two syllables were measured. Result: Lexical stress was marked consistently by duration and intensity but not f[subscript 0]. Lexical stress on strong-weak words was adultlike by 3 years. All 3 measures showed significant differences between adults and children for weak-strong words still present at 7 years. Conclusion: Our findings suggest that protracted development of weak-strong stress production reflects physiological constraints on producing short articulatory durations and rising intensity contours. Findings validate treatment that is centered on strong-weak stress production for children greater than or equal to 3 years with dysprosody. Although intervention for the production of weak-strong words may be initiated before age 7 years, reference to normative acoustic data is preferable to relying on perceptual judgments of accuracy.