Mathematics curriculums worldwide are being refined to prepare students for the twenty-first century by focusing on developing students' higher-level thinking skills. As a result, teachers need to adjust their pedagogical approaches to enact new curriculums, which is frequently facilitated through continued professional development (CPD). During curriculum change, the challenges to fostering effective CPD are often exacerbated, signalling a necessity to understand better how CPD can be structured during reform. This research study aims to design a curriculum resource that acts as a form of CPD, seeking to enhance teachers' use of higher-level thinking questions in mathematics lessons while also gaining a greater understanding of what constitutes effective CPD during curriculum reform. Six Irish primary school teachers in an urban school collaborated for one year with the primary researcher to develop a curriculum resource. Analysis of data collected from observations, focus groups, and researcher field notes guided the iterative design of the curriculum resource. Design characteristics of the curriculum resource and their impact on teachers' practice are discussed. Finally, suggestions for designing and facilitating CPD during periods of change and implications for further research are proposed.