Traditional methods for teaching science courses at the post-secondary level employ a lecture format of instruction in which the majority of students are passively listening to the instructor and jotting down notes. Current views of learning and instruction challenge the wisdom of this traditional pedagogic practice by stressing the need for the learner to play an active role in constructing knowledge. The emerging technology of classroom communication systems offers a promising tool for helping instructors create a more interactive, student-centered classroom, especially when teaching large courses. In this paper we describe our experiences teaching physics with a classroom communication system called Classtalk. Classtalk facilitated the presentation of questions for small group work as well as the collection of student answers and the display of histograms showing how the class answered, all of which fed into a class-wide discussion of students' reasoning. We found Classtalk to be a useful tool not only for engaging students in active learning during the lecture hour but also for enhancing the overall communication within the classroom. Equally important, students were very positive about Classtalk-facilitated instruction and believed that they learned more during class than they would have during a traditional lecture.