--- - |2 Abstract Cultural learning begins early, with infants’ and young children's initial imitations of group‐specific local behaviors. Comparatively little is known about cultural development in older children, whose more advanced socio‐cognitive skills can moderate their decisions about adherence to the established cultural conventions and acceptance of new norms. Focusing on the acquisition of a regional dialect, the current study was conducted in a small community in western North Carolina, whose rich Appalachian heritage grew from distinctive cultural and living traditions. The region has gradually opened up to outside influences and the local culture is now shifting toward mainstream American socio‐cultural norms. The study sought to determine how preadolescents positioned themselves in this socio‐culturally changing environment. Using detailed acoustic analysis to measure stylistic variation in speech in 9–12‐year‐olds and perceptual ratings to verify its salience, we examined the pronunciation of the vowel /ai/ to test children's adherence to the old Appalachian identity marker (the monophthong) and their acceptance of the modern American society (the diphthong). As an innovation, children created an intermediate phonetic variant that reduced the pronunciation differences between the old and modern patterns. Demonstrating the ability to adapt speech style to context, they increased the degree of diphthongization in this /ai/‐variant in careful speech (reading), and reduced it in casual conversations. Girls’ productions were more diphthongal than were boys’ in reading but not in conversations. The new variant in children represents regional dialect levelling, and likely results from their accommodation to the changing environment, which promotes reduction of old marked forms. - Developmental Science, EarlyView.