Since the 2000s, early co-constructive mathematical learning in kindergarten has focused on political discussions and (mathematical-didactic) research. This is because kindergarten is the first place for subject-specific learning, next to socialization in the family. Research on this first institutional learning in the kindergarten often focuses on the interaction between children and elementary school teachers, which is presented as a key variable for these learning processes. However, it is peer interaction that takes up a large part of the day in kindergarten. In these interactions, children negotiate a variety of issues that are relevant to them. The following contribution will present research that focuses on these peer interactions in the context of block play situations. There is a general analysis using methods of (qualitative) thematic analysis as well as a detailed analysis using methods of interpretative classroom research. These analyses will help answer the question as to what role these peer interactions play in early mathematical learning processes and to what extent conditions can emerge in such interactions that enable mathematical learning in the sense of Miller (1987).