The knowledge regarding teacher learning processes is fundamental to organising a professional development (PD) programme systematically and effectively. In the study reported in this article, we examined content-related teacher learning processes in the context of inclusive mathematics teaching. We first explain approaches to inclusive mathematics teaching (derived from the literature) and how these approaches can help teachers to differentiate with open-ended and challenging tasks. While focusing on the transfer of learning as one important part of teacher learning processes, the study investigated teachers' use of the PD content (i.e., the teaching approaches) after a PD session. For this, a case vignette as a method of inquiry was used. We analysed the written answers from 15 secondary teachers using qualitative content analysis. The teachers used many approaches to inclusive mathematics teaching and applied them in the context of the case vignette. Finally, we focus on implications for the design of PD programmes concerning teacher learning about inclusive mathematics teaching.