Inquiry-based science instruction offers great promise as a means of actively engaging students in authentic scientific problem solving, including consideration of research design issues. At the same time, inquiry introduces some difficulties. In particular, familiar “cultural tools” for classroom discourse, such as Initiation-Reply-Evaluation sequences, are no longer appropriate because they are premised on known answers and teacher-driven activity. To help support productive open-ended science inquiry, coaching strategies that allow for strong student voice and teacher influence are necessary. We describe the sociocultural theory motivating one such strategy, transformative communication, as well as a specific dialogue sequence that can be used as a cultural tool for accomplishing such interaction. We then illustrate the utility of the dialogue sequence in four key episodes within an inquiry-based high school Earth Science class. © 2001 John Wiley & Sons, Inc. Sci Ed85:223–238, 2001.