There is a current debate concerning what constitutes evidence of impact on practice resulting from teachers' engagement in Continuing Professional Development (CPD) courses. The authors present two case studies of teachers who have completed a Masters Degree in Education, offering their own perceptions and those of their colleagues on the impact that their studies have had on their work in school. The case studies are based on interviews undertaken shortly after completion of the course and 1 year later, and show different ways in which impact may be demonstrated. It is argued that this has implications for higher education course providers and schools: they need to be flexible in their interpretations of the relationship between professional development and impact. In particular, the authors advocate that they listen to individual stories of the experience of CPD.