The aim is to investigate how encounters with peers affect an individual's meaning making in argumentation about socio-scientific issues, and how the individual's meaning making influences the argumentation at the collective level. The analysis is conducted using the analytical method "transactional argumentation analysis" (TAA) which enables in situ studies. TAA combines a transactional perspective on meaning making based on John Dewey's pragmatic philosophy with an argument analysis based on Toulmin's argument pattern. Here TAA is developed further to enable analysis that in detail clarifies the dynamic interplay between the individual and the collective--the intra- and the inter-personal dimensions--and the result of this interplay in terms of meaning making and learning. The empirical material in this study consists of a video-recorded lesson in a Swedish upper secondary school. The results show that the analysed student is influenced by peers when construing arguments, and thereby acts on others' reasoning when making meaning. Further, the results show that most of the additions made by the analysed student are taken further by peers in the subsequent discussion. This study shows how an individual's earlier experiences, knowledge and thinking contribute to the collective meaning making in the classroom.