In this paper we describe Classroom Presenter, a Tablet PC-based system that facilitates active and collaborative learning in the classroom. In our setup, both the instructor and the students are equipped with tablet computers. At various points during a lecture, students are asked to solve a problem or answer a question. In response, students write their solutions on the tablets and submit them wirelessly to the instructor. The instructor can view all responses, select one or more to display to the class, and annotate responses with ink as they are being displayed. Since Fall 2004 we have piloted the system in eight Computer Science courses at the University of Washington. Here we will describe the system and our initial experiences in the classroom.