The article considers early childhood mathematics learning from an interactionist perspective. Here, mathematics learning is differentiated into two aspects: the acquisition of mathematical concepts and procedures in terms of learning mathematical content, and the development of mathematical thinking in terms of learning to reason. This contribution focuses on the second aspect. Based on interactionist perceptions of mathematical learning, the development of mathematical thinking is described as increasing participation in mathematical discourses. For a more detailed description of these discourses, the so far common focus of interactionist approaches to mathematics learning on the analysis of mathematical negotiation of meaning is expanded to include a description of emerging argumentative structuring of the mathematical negotiation processes. In the empirical analyses forming the basis of this article, different discourse styles are reconstructed utilizing this theoretical extension, which we call narrative, formal, and narratory discourses. In future research, they will be used as a theoretical basis for the reconstruction of the development of mathematical thinking.