This article describes a strategy for instructing graduate teaching assistants and presents results on how the program influenced their conceptions of teaching science. The discipline-specific seminar was designed to help teaching assistants learn how to effectively communicate biology content to undergraduate students, and aimed at increasing teaching assistants' awareness of discipline-specific teaching strategies. Topics included the current state of undergraduate teaching and learning, alternative strategies, students' conceptions, specific teaching strategies related to biology topics, and innovative approaches. An open-ended questionnaire was used to explore how graduate students define the teaching of science. Results indicated that after the seminar graduate teaching assistants changed their conceptions of good science teaching to include knowing pedagogical strategies. Results also indicate that as a result of the seminar the teaching assistants recognized that (1) conceptual understanding is the basis of learning, (2) learning is more of constructing individual understanding and their role should be to facilitate, (3) planning is much more than reviewing the material, it is necessary to understand pedagogical strategies to help students understand the material, and (4) learning is an active process of constructing knowledge. (JRH)