This article examines the way in which socially constructed notions of "language", "social cohesion" and "diversity" create tensions within different educational arenas, particularly concerning educational policies developed at administrative levels and the subsequent interpretation of these policies in the classroom. Specifically, the article looks at the different production and reproduction processes of an official policy concerning "language and integration", aimed at the immigrant population in Catalonian schools (Spain). The method used combines conversation analysis with text analysis of official documents in order to find traces of interdiscursivity between texts and practices. While the focus of the article is based on a case study of conceptualisations of languages, social cohesion and cultural diversity in two classrooms in Barcelona, it is generally relevant to the world of education, especially as the rate of population movements worldwide has increased significantly in recent years. (Contains 2 notes.)