ABSTRACT
The topic of change and development is the central issue for developmental psychologists, including especially those of us concerned with cognitive development. After rather a prolonged period during which many developmentalists appeared to abandon the idea of cognitive change in favor of models based on invariant processes and structures across the lifespan, theorists seem ready again to face the obvious: Knowledge systems change dramatically during childhood and adolescence. The important questions are what changes, how, when, and why. In this chapter I reflect on the ways that these questions have been raised in my own work, especially on aspects of that work that have been addressed to what changes and how, and on what I have learned from the process.
