Challenging the notion that English-medium instruction (EMI) is necessarily an English-only space, the authors argue for an alternative vision of EMI settings as spaces that benefit both emergent bi/multilinguals and their English-monolingual peers. Given that the enactment of EMI varies according to the underlying language ideologies of the educators who implement it, the authors argue for the importance of shifting from deficit-based monogolossic ideologies to more asset-based heteroglossic ideologies and of creating heteroglossic "implementational spaces" (Hornberger, 2005, p. 605). In such spaces, all students, particularly emergent bi/multilinguals, are encouraged to act as agents, strategically drawing upon the full range of their semiotic repertoires (Kusters, Spotti, Swanwick, & Tapio, 2017) in order to participate, learn, and contribute as full members of the classroom community. In this context, the critical question is how such heteroglossic practices can actually be enacted by teachers who are themselves not bi/multilingual. As a contribution to answering this question, the authors present two promising examples from two independently conducted qualitative studies, which were carried out in EMI mainstream classrooms in U.S. elementary schools, to show how such spaces might be actualized in practice. Then, using them as a point of reference, the authors discuss key issues in fostering and sustaining such spaces, and offer recommendations for teachers and teacher educators.