Research has indicated that most science classrooms are not intellectually demanding and place little emphasis on small group discussions and laboratory activities. However, successful science programs and competent science teaching that can provide models for other science teachers do exist. This study sought to document the teaching practices of two exemplary biology teachers of grades 11 and 12 by means of an interpretive research methodology. Both teachers had a thorough and comprehensive knowledge of the content they were to teach and had a range of teaching strategies that could be used without a great deal of thought. Their expectations for student performance were high, consistent, and firm. Students were expected to complete a high level of academic work in discussions, in problem work, and in laboratory activities, and were encouraged to take responsibility for their own learning. A distinctive feature of these biology classes was the high level of managerial efficiency, where lessons were busy occasions for both teacher and students; students had little opportunity for off-task behavior. Both teachers actively monitored the behavior of both high- and low-ability students by moving around the room and speaking with individuals, while still maintaining control of the entire class. By manipulating questioning and the social environment, both teachers encouraged students to engage in work, gave effective praise to the whole class and to individuals, encouraged student input by referring to it, helped students to effectively use their time, and gave marks for completion of set work. Compared to research with less-successful teachers, these teaching behaviors contributed to exemplary practice.