Judith has decided to become a biology teacher, and she knows that she has a lot to learn. After all, an expert teacher draws on a considerable fund of knowledge about teaching, in addition to knowledge of the subject matter (Shulman, 1990). At the same time, Judith does have at least some knowledge about teaching and learning. She has her own ideas about education, ideas that might be called “intuitive” conceptions, to contrast them with the “disciplinary” conceptions to which Judith will be exposed in teacher-education courses. Even people who are untrained in education hold powerful intuitive/tacit conceptions about teaching and learning, and these intuitive conceptions exert a great deal of influence on the way those people think and act with respect to education.