Emerging digital technologies offer a transformative potential to redefine learning tasks and many examples of this potential are now available. The scaling of the innovative pedagogies emerging from the research into widespread and sustainable practice, however, remains problematic. This paper addresses the issue of scaling by using Design Based Research (DBR), also known as Educational Design Research, within teacher professional development to reposition teachers' thinking about the place of digital tools in their teaching. Using a project seeking to support the use of new digital technologies to develop children's spatial reasoning as a 'worked example', this paper highlights how the bringing together of the knowledge of educational research and knowledge of teaching practice in DBR can provide a catalyst for epistemic change. The paper will argue that DBR positions the knowledge and practice objects of both research and teaching as 'epistemic' or 'not yet known' objects and, therefore, the legitimate focus of experimentation and reflection.