Currently, there is no research-based evidence to guide teachers of English in Sweden as to whether and how to use students’ background languages to facilitate learning, participation and engagement (Author & Others 2017). Existing research shows beneficial effects of providing L1 (mother-tongue) translation equivalents of English vocabulary (Lee & Macaro 2013; Prince 1996), of teacher code-switches into students’ L1 for learning English grammar (Kupferberg & Olshtain 1996; Rolin-Ianziti & Brownlie 2002), and of translanguaging pedagogy (Cummins 2017; Paulsrud et al. 2017). This research also reveals a lack of studies in English classrooms in Scandinavia. The prior research in English classrooms was carried out in other parts of the world, and in all cases students shared the same L1. The present study breaks new ground by focusing on classrooms with diversity in students’ L1 backgrounds, reflecting growing multilingualism in Scandinavia (Dahl et al. 2018; Paulsrud et al. 2018). Based in theory of teachers as policy makers (Menken & García 2010) and in bilingualism research (Baker & Wright 2017), our project focuses on the teaching and learning of English in multilingual Swedish schools (students aged 13-16). In this paper, we report results of a case study (Duff 2008) conducted within a larger project (Author & Others 2017). Participants are one English ‘excellent’ teacher (förstelärare) and two student groups: a mainstream (23 students) and a fast-track (21 students) English year-8 class. Using ethnographic methods of classroom observation (14 lessons), photography, questionnaire and interviews (the teacher and 18 students of different L1 backgrounds), we address the following questions: 1) To what extent and for what purposes does the teacher draw on students’ background languages when teaching English?, and 2) What are students’ beliefs about their teacher’s use of English and other languages in English lessons?. Data analysis reveals that the teacher used mainly English (the target language), but also Swedish (the majority language in Sweden and school language), although sparingly, to translate vocabulary, explain grammar, communicate task requirements and grading criteria. The interviews drew on the shared experiences of the observed lessons (where researchers and students were co-present) and revealed that students were highly aware of their teacher’s code-switches, and that students with a lower proficiency level in English stated that they benefited from receiving information in both English and Swedish. An important implication is that the students believed that their teacher’s code-switches served to facilitate their literacy development in English and in Swedish.