The monolingual tradition of the compulsory school subjects Norwegian/Swedish is challenged by knowledge developed in the rather new academic disciplines of Norwegian/Swedish as second languages. A point of departure in this study is an argument that knowledge about multilingualism and second language learning needs to be part of the school subjects not only because the classrooms include an increasing number of multilingual students, but also because all students growing up in societies influenced by globalization and migration need to learn about new language practices. Cross-linguistic perspectives might open new ways of understanding linguistic phenomena and students’ own language(s). The study uses the concept of “powerful knowledge” (Young 2009/2016) in examining the content of the school subjects. An overall question is how knowledge from the above-mentioned academic disciplines is transformed in printed textbooks for middle school in the two countries. A central part of the study is a concept-focused content analysis of topics of language diversity found in middle school textbooks published between 2006 and 2017. Although there are differences between the two countries, a main result is that the textbooks themselves offer students few possibilities to learn about second-language learning, multilingualism and comparisons between languages. Examples from other languages than Norwegian/Swedish occur occasionally, but the languages chosen do not reflect the main languages spoken by immigrant groups. However, some of the assignments found in the textbooks invite students to enter roles as experts, empathetic persons or active citizens (cf. Otnes 2015) and seek knowledge from other sources while working on the content. In this paper, we analyze these assignments and discuss their potential in making students discover new ways of thinking and go beyond the limits of their personal experience, cf. Maude’s (2016) discussion of identifying knowledge as powerful in Geography.