This study represents a first effort to identify sociocultural background variables that predict the successful mastery of a heritage language by adult learners. While there are well-documented sociocultural models for other second language learners, thus far there are no similar published models for heritage language learners. We focused on Latino college students learning Spanish (N = 55) and the following background variables: cultural identification, cultural participation, and use of Spanish outside of class. Language assessments focused on learners' mastery of Spanish accent and grammar. Results indicate that these background variables are related to mastery of Spanish accent, and that use of Spanish outside of class is related to mastery of Spanish grammar. The findings have important implications for language instruction and point to a number of important future research directions in the field of heritage language learning and instruction.