Argumentation and modelling are core scientific practices, and studies suggest that incorporating the specific practices in the teaching of science can engage learners. This is a qualitative study of a classroom of 10-12-year-old students working collaboratively in argumentation and modelling. The aim of the study was to explore how primary school students use their models whilst arguing about a socio-scientific issue and to explore whether and how the process of arguing is linked with the modelling process. In order to explore the aforementioned, a learning environment was designed to help students participate in the epistemic practices of argumentation and modelling. Our findings indicate that the students engage in argumentation by providing rebuttals, and there is an intersection of higher-level modelling cognitive processes and higher-level argumentation epistemic aspects. We hypothesize that the use of models might have contributed to high-level argumentation. Our findings point to the idea that if we want science teaching and learning to be more productive even for younger students, we should be developing the epistemic practices of modelling and argumentation in unison as a way to promote and support both practices and as a consequence to promote both content learning and reasoning skills.