For the purpose of analyzing the longitudinal development of mathematical thinking, statuses of participation of a child are reconstructed and theoretically described in terms of the framework of the “Interactional Niche in the Development of Mathematical Thinking.” In this chapter, we deal with the concept of adaptability within this framework, which we consider as having a twofold characteristic. The interactive process of negotiation of meaning adapts more or less to the needs of the participating children, thus producing specific options of participation and conversely the children adapt more or less successfully to the then accomplished content-related requirements. We demonstrate our theoretical reflections by presenting two episodes of a case study of a child, whom we accompanied in her mathematical development over a period of about 3 years.