The Kuhn and Pease (p. 279, this issue) article advances the fields of cognitive development and learning by integrating work on executive functions, metacognition, and scientific reasoning. The article also expands developmental work to older children and adults, to personal beliefs, and to social information, and reinvigorates the construct of metacognition by identifying its role as a mechanism of development. Limitations of the study, for example, the lack of an assessment of the strength of the participants' initial beliefs about the problem, suggest fruitful directions for future research. A final discussion examines ways in which the Kuhn and Pease account of the role of executive functions in learning could be broadened.