The coordination of beliefs, norms, and behaviors is foundational to theories of group formation. However, because beliefs and norms are not directly observable, signaling mechanisms are required to build reliable signals of latent traits. Although the mathematical theory behind these signals is robust, there is very little testing of ethnic marker theory or of its key propositions that markers become more prevalent along ethnic boundaries and where more than two cultural groups are in contact. We present an ethnographic test of (...) this theory with phonetic differences serving as potential group signals. The data derive from an ethnographic and linguistic investigation in two contrasting secondary school settings in Utah, one that is majority European American and one that is ethnically more diverse. Word list recordings were collected as part of interviews with teens from different backgrounds. We extracted acoustic data from the speech of European Americans (EAs) and Pacific Islanders (PIs), then analyzed differences in the pronunciation of the vowel in words such as “bit.” We found evidence of greater phonetic marking at the more diverse school, along more prominent boundaries of ethnic interaction. These results align with predictions made by the theoretical models. This initial empirical test of model predictions provides justification for the development of more complex models that could account for more variables within the environment. (shrink)