The Engineering Communication Program at the University of Toronto has recently begun using engineering graduate students as Communication Instructors (CIs) in the Mechanical Engineering portfolio courses and our work in the Mechanical and Industrial Engineering capstone design courses. The move was an attempt to bridge the discipline chasm between communication and disciplinary expertise; this paper begins to document the impact of this interdisciplinarity. Through an analysis of narratives of CI experiences using Engeström’s model of activity theory, we narrowed our focus to an exploration of the changing rules and division of labour that occurred over the duration of the courses. We found that while students and CIs bring different understandings of rules and division of labour to the work, these elements can be changed—and that affect plays a key role in the changes.