In light of Chinese language diversity, it is important for Mandarin teachers to demonstrate an accurate understanding of language variation and critical pedagogy, empowering and embracing all emergent bilingual students and incorporating recognition of those learners whose heritage languages are alternative Chinese varieties. While Standard Mandarin is often referred to as 'Chinese', other varieties are usually called 'fangyán' or 'dialects', a misleading translation causing confusion in both public and educational fora. In this study, I investigated pre- and in-service Mandarin Chinese teachers' developing language and teaching ideologies regarding Chinese varieties in the U.S. context. Participants were 30 Chinese natives from a graduate language education programme in the United States. They represented three Mandarin teaching stages: beginning and advanced-stage students, and recent graduates teaching Mandarin in the field. Data came from 60 semi-structured interviews, two with each participant. Framed by constructivist grounded theory and viewed through the lens of critical theory, results revealed participants' complex ideologies and their evolution across the three developmental stages related to sociolinguistic notions regarding Chinese varieties. Participants' views about teaching often reflected the realities of the educational and social cultures in which they participated, revealing the importance of acquiring a strong foundation in sociolinguistics.