Research has suggested that system-wide professional development needs to embrace ongoing and sustainable processes such as critical reflection, being within a community of practice and the co-creation of new practices within and across early childhood systems. However, there is little research on how professional development can be designed in a personally meaningful way to support sustained learning. The research reported here is part of a wider study on the professional development of early childhood teachers. Video observations of one teacher's interactions with children and interviews with that teacher are analysed to investigate how Chinese early childhood teachers' professional development may be meaningfully designed through an Educational Experiment (EE). A Conceptual PlayWorld model as the intervention for the educational experiment was used to create new conditions. The theoretical problem for teachers and researchers was how to bring new play practices into kindergarten programs. We argue that the educational experiment creates a new kind of social situation for teachers, amplifies reflective practice and in so doing, acts as an important source of professional development for sustained practice change.