Teachers who teach content to immigrant language learners are often asked to attend explicitly to linguistic features of texts dealing with disciplinary knowledge. This study uses the theoretical frameworks of Systemic-Functional Linguistics and Legitimation Code Theory to explore the role of language, more specifically technical terms, grammatical metaphors, and genre structures, in knowledge building. The study is based on observations and voice recordings during a curriculum area about maps and population in grade 6 with the participating teacher employing genre-based pedagogy. The studied interaction shows that an initial focus on technical terms within the field of geography in later phases shifts to features of language: genre structures, logical connections and instances of grammatical metaphors. However, these features of language are modelled in texts and wordings belonging to everyday experience rather than disciplinary knowledge. By closely examining the relationship between field knowledge and metalinguistic knowledge, the study contributes to the discussion about the role of language in content learning.