This study examined the phenomenon of student teachers' practical knowledge of what constitutes a successful classroom lesson. One student teacher's personal orientation of practical knowledge and implicit understanding of what is needed to make sense out of the experience of success in classroom lessons was explored before and after the student teaching experience. Tentative conclusions are presented in the form of hypotheses: (1) student teachers hold a limited number of constructs which they use to interpret a successful lesson; (2) the closer an actual lesson is to matching constructs of success, the more successful it is deemed; (3) perceptions of success change over the course of student teaching; (4) lesson plans and teaching strategies are developed to bring about success; (5) an implicit image of success is held by student teachers; (6) student teachers have practical knowledge of a successful lesson; (7) there is a congruence between what is understood as success and what a student teacher knows or learns to do to bring it about; and (8) experience provides student teachers with knowledge of results. A discussion of these findings includes consideration of their implications for preservice teacher education. (JD)