This study examines how a PD program to promote teachers' shift toward a student-adaptive pedagogy impacts students' multiplicative reasoning. We describe the underpinnings of this pedagogy and main components of the PD program. Then, we present key features of participants, data collection/analysis methods, and the written assessment used to measure students' multiplicative reasoning (MR). We found a significant increase in students' MR, between (a) year-ends for different classes and (b) year-start to year-end for the same groups of students. We also found students of participating ("treatment") teachers outperformed those of non-participating ("control") teachers. We discuss the importance of these findings for theory, for teacher education, and for students' mathematical future. [For the complete proceedings, see ED606531.]