The quest to improve teaching on a wide scale is an enduring challenge globally. Yet demonstrable improvement in teaching quality is both elusive and slow. In this essay, I explore some of the complexities that contribute to the slow pace of change, including: the slippage between teachers and teaching as the object of improvement; the poorly defined concept of good teaching; the difficulty of demonstrating improvement in teaching; institutional constraints on improvement efforts; the growing web of marketing; and conflicting conceptions of professional development itself. Using my ongoing work on Quality Teaching and Quality Teaching Rounds, I illustrate how we have addressed these matters to produce measurable and sustainable effects. Finally, I elaborate the key principles of our approach, while acknowledging the challenges of wide-scale improvement, given the institutional and discursive character of the field.