While several studies have investigated English-medium instruction (EMI) or content and language integrated learning (CLIL) in Swedish upper secondary and tertiary education, few have investigated such programmes in Swedish primary schools. This paper explores perceptions among staff and students about affordances and constraints in the learning of content and languages, drawing on data from a larger longitudinal case study of an English-Swedish bilingual primary class during Grades 4-6. Data consisted of semi-structured interviews with a school leader, 12 teachers and 22 students as well as fieldnotes and photographs from classroom observations. Thematic analysis of the data revealed the belief among staff that learners acquired English naturally by being ‘forced’ to use it in English-medium subjects taught by native speakers of English. The use of Swedish among students in these subjects was generally seen as a potential scaffold when communicative difficulties arose, as students who were more proficient in English could translate and provide their classmates with explanations of difficult concepts in Swedish. However, staff and students nonetheless voiced concerns about students’ content learning as well as about limited development of subject-specific language in Swedish, which could have implications for their future Swedish-medium studies. Meanwhile, although multilingual students’ mother tongues were valued by the students themselves, participants did not acknowledge them as legitimate learning resources for use in the mainstream classroom, where only English and Swedish were allowed to be used in interaction.