This article focuses on mother tongue teaching in Arabic, Dari, Pashto and Somali as it is practised in a linguistically diverse primary school in Denmark. The article draws on a linguistic ethnography of language teaching across the curriculum, and the analysis focuses on three mother tongue teachers. Drawing on classroom observations and interviews with teachers and children, the article through three cases portrays mother tongue teaching as an inherently tension-filled language ideological practice. The tensions revolve around negotiation of what counts as legitimate and appropriate language(s): What counts as Arabic when Kurdish-speaking children enter Arabic class? How do centuries of language ideological tension between Dari and Pashto in Afghanistan resonate in mother tongue teaching in Denmark? How is dialectal variation in Somalia handled in mother tongue teaching of Somali in Denmark? The language ideological tensions extend across time and space, across generational borders and across hierarchized roles and relations between children and parents, between pupils and teachers, between teachers and school management and across the mother tongue teachers' various personal and professional identities as teachers, parents and authors. Mother tongue teachers thus navigate between ambivalent and contradictory language ideological orientations as an integral part of their teaching practice.