This article employs a language ideological framework to explore how particular language attitudes and beliefs shaped one group of U.S. students' choices to avoid producing a dialectal variant, Castilian Spanish [theta], in the context of an undergraduate Spanish pronunciation class. An analysis of ethnographic data points to the significance of three common beliefs that frame the appropriate use of [theta] in idealized monolingual terms that are incongruous with a U.S. national identity. The instructor mobilized these beliefs at key moments to establish normative expectations that discouraged learners from producing [theta]. Students also alluded to these beliefs and the consequences of being unable to use [theta] appropriately to explain their decisions to eschew this variant following the class. These findings suggest that language attitudes and beliefs shape learners' choices to adopt dialectal variants in production as an effect of language ideologies on the L2 development of phonology and sociolinguistic competence.