<p>This study examines how a mathematics teacher, whose noticing skills developed through a 2-year online professional development program, implemented responsive teaching moves in a classroom setting while teaching the concept of the mean. Accordingly, the study was built on the responsive teaching model, which stems from noticing students’ mathematical thinking. After discussing various scenarios involving student strategies for alternative mathematics content with 30 other participating teachers in an online environment, a teacher with eight years of professional experience implemented two tasks related to the concept of the mean in two sixth-grade classrooms. The analysis revealed that the teacher employed responsive teaching moves, albeit in varying orders, with different frequencies, and at varying durations. This led us to conclude that a sustained professional development program focused on developing teachers’ noticing of students’ thinking appeared to improve teachers’ in-the-moment responses regarding the concept of the mean.</p>