This paper illustrates that focusing on processes of interaction is crucial to a closer understanding of mathematical learning processes in mixed-ability groups. In doing so, the paper's focus is on expounding a theoretical-methodological framework of an interactionist perspective in mathematics education. This framework interlinks sociological and social-constructivist theories with subject-specific educational theories. As a result of two examples of analyses it becomes apparent that investigations on mathematics learning within linguistic negotiation processes, based on an interactionist-oriented theoretical frame, provide in-depth insights into individual learning possibilities of a diverse student body. These insights are made possible only by means of a detailed micro-sociological examination of collectively occurring learning processes within linguistic negotiation processes.