<p>This study investigated the effects of an innovative professional development program aimed at enhancing teacher noticing skills and related professional knowledge in inclusive mathematics education in secondary algebra instruction. A total of 653 participants from three experience groups with different length of teaching experience, namely master’s students, teachers in preparatory service, and in-service teachers from Germany, participated in a pretest–posttest evaluation design that included a control group. The professional development program comprised 18 hours of coursework designed to facilitate teacher noticing skills by integrating novel teaching materials and video-based learning activities that combined both mathematics pedagogical and general pedagogical perspectives. The results indicated significant improvements in teachers’ noticing skills and related professional knowledge for the intervention group across all investigated facets, particularly for teacher noticing under a pedagogical perspective and mathematics pedagogical knowledge, compared to a control group that exhibited no significant changes. Effect sizes ranged from small to medium, suggesting that the professional development program effectively improved participants’ knowledge of inclusive teaching and their abilities to perceive, interpret, and make decisions in inclusive contexts. Notably, master’s students exhibited the most substantial gains in all competencies, while in-service teachers primarily improved their teacher noticing from a pedagogical perspective. The findings underscore the importance of tailored professional development for fostering teacher noticing in inclusive mathematics education and yield valuable insights into this area of teachers’ competencies.</p>