One of the central concerns of English as a Second Language (ESL) education within many English-speaking countries has been the relationship between content and language teaching. In Victoria, a state of Australia, the educational policy of mainstreaming ESL is presented as a means of catering to the language learning needs of ESL students within mainstream subject contexts through the integration of the language and content curriculum. In such policy, the relationship between language and content is constructed as unproblematic and uncontested. This paper analyses, using appraisal theory [Martin, J. R. (2000). Beyond exchange: Appraisal systems in English. In S. Hunston, & S. Thompson (Eds.), "Evaluation in text" (pp. 1--42). London: Oxford University Press] and positioning theory [Harre, R., & van Langenhove, L. (1999). "Positioning theory: Moral contexts of intentional action." London: Blackwell Publishers], the planning conversations of an ESL teacher and a science teacher planning curriculum for a year 10 science class. The analysis highlights the factors that influence the extent to which the teachers can balance language and content, including power relations between teachers, the curriculum topic under discussion and the dichotomy that is constructed by the teachers between language and content. Implications for language and content research will be highlighted in light of the conclusions drawn from this study.