Currently in Germany, there are increasing numbers of primary schools who install multi-age education for pedagogical reasons or due to demographic changes in rural areas. Especially for mathematics education, this often causes individualised learning to take place. However, as interaction is seen as a foundational constituent of mathematical learning (Miller, 1986), this research focuses on pupils’ interactions within multi-age mathematics education and has the objective of describing how pupils of different ages learn collaboratively. Because learning is seen as the increasingly autonomous participation in collective argumentation, we seek to identify how pupils participate in processes of collective negotiation of meaning and, thus, examines interaction by using the analysis of argumentation and the analysis of participation.