Dispositions are the engine of performance in teaching, linking inner values and commitments with action in the context of practice. This article presents a theoretical conception in conjunction with an individual case study of the process by which dispositions develop and function in teaching. Focusing on teaching that is ambitious both in its intellectual goals and in its concern for the learning and well-being of all children, this article argues that dispositions can be understood as "performances of understanding" that are developed over time, influenced by context, integrated into the array of dimensions of learning to teach and emerge within professional communities. It is based upon a longitudinal research study that tracked two cohorts of 10 beginning teacher candidates through their undergraduate teacher preparation experience. (Contains 3 figures, 1 table and 2 footnotes.)