Teachers’ professional noticing—often conceptualized as their situation-specific skills of perception, interpretation and decision-making—constitutes an important component of their professional competence. Noticing has become increasingly significant worldwide in the pursuit of inclusive mathematics education in classroom settings, whereby teachers are required to provide equal opportunities for students across all ability levels. However, current teacher noticing frameworks lack the requisite specificity to support inclusive mathematics education, particularly regarding diagnostic applications and adequate learning support, and thus a revision of existing frameworks is warranted. On the one hand, such frameworks must incorporate selected facets of teacher knowledge, including mathematical pedagogical content knowledge (MPCK) and general pedagogical knowledge (GPK) specified for inclusive teaching; on the other hand, the differentiation into dispositions and situation-specific skills as decisive components of competence viewed as a continuum must be considered, as Sigrid Blömeke et al. suggested in their seminal framework. This paper describes the methodological challenges associated with the development of standardized instruments to measure teachers’ professional knowledge and noticing within inclusive mathematics education, as undertaken by the project Teacher Education and Development Study – Inclusive Mathematics Education (TEDS-IME). Using a large sample of 628 pre-service and in-service teachers, the paper aims to examine the dimensionality of teachers’ competence for inclusive mathematics education and expert–novice differences in the pattern of their competence facets. Our findings indicate that the newly developed video-based instrument for teachers’ noticing in inclusive mathematics education serves as a reliable and multidimensional measurement for both pre-service and in-service teachers.