This paper explores the ethical challenge of the mandate for educational change within professional development. Drawing on a long-term educational design research project focused on problem solving and problem posing, we examine how collaboration between researchers and teachers evolves across four phases. Initially, researchers led the design and implementation. Over time, teachers became active co-creators, contributing to planning, data collection, and analysis. This shift from research on teachers to research with teachers enabled a shared mandate for change, fostering sustainable professional development. Our findings suggest that change is more likely to occur and sustain when it originates from within the teachers themselves, supported by collaborative structures. The study highlights how educational design research can bridge ethical concerns and promote teacher agency in relation to change.