Central to criticisms of teacher professional development is an insufficient focus on its impact including minimal evidence of changes to practice coupled with inadequate emphasis on student outcomes. This year-long study of one case study school investigates the impact of a seven-month professional development initiative designed to support teachers in implementing a reform approach to mathematics teaching. Data sources include teacher interviews, lesson observations, student focus group interviews, and document reviews. Findings suggest initially impoverished mathematics experiences that later begin to show signs of enrichment. Students' insights into changing practice indicate that students want to be challenged more in mathematics and experience this challenge in inclusive learning environments where all students are valued and supported. A key finding is the effectiveness of student insights in increasing teachers' engagement with the professional development initiative and in motivating teachers' engagement in, and commitment to, the reform process. These findings highlight the complexity of the teacher change process, in particular, how cognitive dissonance plays a key role in changing practice. Central to creating this cognitive dissonance were students' insightful perspectives about learning mathematics. This research contends that student voice can provide unique context-specific insights yet is under-utilised in professional development theory and practice.