Students are experts at sizing up instructors, but many do not extend this analysis to non-instructor audiences, which can reduce their effectiveness in new communication situations. Audience, therefore, is a crucial threshold concept not only in Rhetoric and Composition, but in any discipline that values communication skills. How can instructors help students develop a deeper understanding of audience in the disciplines and begin to cross the threshold? In this article, I describe how a group of Professional Writing and Rhetoric students engaged the audience threshold through a semester-long, client-based project. Drawing on data collected via reflections and portfolios, written deliverables, client feedback, and instructor notes, analysis shows the students were initially overconfident in their ability to assess audiences, worked through valid emotional responses to substantive client feedback, and learned to negotiate the dynamics of multiple audiences more carefully over the course of the semester.