The focus of this article is upon progression in the curriculum, its relation to a particular psychological model, and implications for policy and practice. The illustrative case is the National Curriculum for England and Wales. Focusing primarily upon the history and the science curricula, the author offers and justifies the idea of a threedimensional model for the curriculum to account separately for profiles in acquiring knowledge in a variety of contexts, and for progress in the ability of students to handle increasingly complex concepts. Without a theoretically justified notion of progression, the author concludes that the implementation of the National Curriculum, including its assessment procedures, will continue to be problematic.