Systematic reviews and meta-analyses of the research literature on continuing professional development and School Improvement demonstrate that teachers who have the opportunity to develop "knowledge of practice" by integrating theory and practice have a positive impact on student attainment. It is argued in this article that we have sufficient weight of evidence to indicate that engaging in curriculum development as a participant in a community of inquiry is the optimal context for professional learning to develop knowledge "of" practice. However, establishing participation in communities of inquiry as integral to teachers' professional learning remains a challenge and we need better ways of sharing and interrogating what we (think we) know. Examples of "experiments in practice" to promote professional learning and make a difference in the Religious Education classroom, are used to indicate what has worked and what has not and what we might do next.