This chapter focuses on learning activity that was suggested by El’konin and Davydov as a framework for teachers to design opportunities for students to emerge collective mathematical reasoning. The data for the chapter were taken from a 3-year longitudinal research project in which learning activity was used to design teaching, tasks and learning models in a multicultural and multilingual Swedish primary school. As a result of using this framework, a situation was highlighted whereby the learning models specific to learning activity had been constructed by second-language students aged 6 and 7 years as they emerged collective mathematical reasoning that focused on comparing two different quantities. The contribution to previous research concerning how learning models can be used in such student groups for collective reasoning about relationships between quantities is twofold; that is, (1) the use of the learning models can help students and teachers to return to the problem they have jointly identified in the collective reasoning and (2) the use of the learning models can help students who struggle with different linguistic dilemmas to jointly reflect on both their own and others’ arguments.