My goal in writing this book is to change the agenda of the field of cognitive development. In particular, I want to promote greater attention to the question that I believe is inherently at the core of the field: How do changes in children’s thinking occur? Focusing on change may not sound like a radical departure from current practice, but I believe it is. It will require reformulation of our basic assumptions about children’s thinking, the kinds of questions we ask about it, our methods for studying it, the mechanisms we propose to explain it, and the basic metaphors that underlie our thinking about it. That modifications of all of these types are being proposed as a package is no accident. Just as existing approaches have directed our attention away from the change process, so may new ones lead us to focus squarely on it. This concluding chapter summarizes the kinds of changes in assumptions, questions, methods, mechanisms, and metaphors that I think are needed. My initial decision to write this book was motivated by a growing discomfort with the large gap between the inherent mission of the field—to understand changes in children’s thinking—and most of what we actually have been studying. As I thought about the problem, I came to the conclusion that existing assumptions, methods, and theories acted in a mutually supportive way to make what we typically do seem essential, and to make doing otherwise—that is, studying change directly—seem impossible. Even approaches that proclaimed themselves to be radical departures from traditional theories maintained many fundamental assumptions of those theories. An increasing body of empirical evidence, however, indicates that some of the assumptions are wrong and that the way in which they are wrong has led us to ignore fundamental aspects of development. In this section, I describe prevailing assumptions regarding variability, choice, and change, and propose alternatives that seem more consistent with empirical data and more useful for increasing our understanding of how changes occur.