A pressing issue in education is when to use students’ multilingual repertoires to enhance learning and promote equity (Cummins 2017). Research through the lens of translanguaging (García, 2009) reveals cognitive and social benefits associated with multilingual practices (e.g. García & Kleyn, 2016). There is little research in secondary-school contexts, however, and none in mainstream English-as-an-additional-language (EAL) classrooms in Sweden. International research in secondary schools also suggests beneficial effects of ‘target-language-mainly’ practices (Corcoll López & González-Davies, 2016; Lee & Macaro, 2013) in combination with multilingual strategies, although this research involves cases where students and teachers shared the same L1. The present study breaks new ground by researching a language-diverse, secondary-school EAL classroom, using mixed research methods to understand the multi-causality nature of classrooms (Baker & Wright, 2017). We combined linguistic ethnography (Copland & Creese, 2015) with a pseudo-experimental intervention in an urban, multilingual secondary school. The intervention entailed three different language-practice conditions: monolingual (English only), bilingual (English and Swedish) and multilingual (English and all students’ home languages). Participants were the teacher, her students (N=27, aged 14-15, 11 different home languages) and two researchers. Data include participant observation, audio and video-recorded lessons, photography, classroom learning materials, questionnaires and interviews. In analysis, we applied concepts rooted in multilingualism research: ‘language dominance’, ‘age of onset’, ‘home language’, ‘majority language’ and ‘school language’ (Baker & Wright 2017) and the Nexus Analysis (Scollon & Scollon, 2004) concepts of ‘historical body’, ‘discourses in place’ and ‘interaction order’. Most students expressed positive attitudes toward English-mainly multimodal practices involving the judicious use of Swedish for explaining vocabulary, grammar, knowledge requirements and grading criteria. Some students welcomed opportunities to use their home language in addition to Swedish. Results are explained by students’ need for bilingual English-Swedish language practices to support their developing academic literacy in both these languages at school.