Increasingly, mainstream teachers rather than specialist language teachers (English as a Second Language, bilingual teachers) are expected to work with English language learners (ELLs) in their classrooms. This reality has drawn attention to the quality and content of the teacher preparation for this group of ELL teachers. Situated within this framework, this article problematizes an acceptance of mainstream classrooms as English-only, monolingual learning environments in mainstream teacher preparation. While English is the dominant medium of instruction in mainstream classrooms, a monolingual approach is problematic as it fails to draw attention to the role that ELLs' native language resources play in learning.The article thus advocates for ensuring that mainstream teachers embrace and know how to engage in bilingual practices, broadly defined.