This study explores how students in a joint process of knowledge construction through the use of multilingual and multimodal resources in groups promotes the learning of scientific concepts in the context of laboratory work. Inductive qualitative discourse analysis was conducted to examine how students’ translanguage in a group completing tasks in two Grade 10 secondary science labs (biology and chemistry) in a Hong Kong EMI secondary school and how such a joint process of knowledge construction promotes the learning of scientific concepts. Using translanguaging as a theoretical framework, the analysis shows that even though schools have imposed an English-only policy, students use their linguistic and semiotic resources to both co-construct their scientific knowledge and practise their science apprenticeship. Translanguaging plays a role in mediating the students’ understanding of science, facilitating peer work and creating an enjoyable learning environment in the lab. The result implies that translanguaging as a pedagogical tool may create a space for content subject learning in Hong Kong EMI school setting. Copyright © 2021 Taylor & Francis Ltd.