The emergency department (ED) is a challenging fast-paced environment with high-acuity, undifferentiated patients who often require extensive interdisciplinary care. This paper introduces ExpandED, an expansion pack to the serious board game GridlockED, designed to enhance players' understanding of interprofessional collaboration in the ED and the diverse scope of practice of different ED professionals including physicians, residents, registered nurses, registered practical nurses, social workers, occupational therapists, and physiotherapists. This investigation evaluates the effectiveness of ExpandED as a teaching tool for medical and allied health professions students about interprofessional collaboration in the ED. A program evaluation harnessing a playtest framework was employed. Participants completed pre- and postgame surveys including quantitative measures (e.g., Likert scales) and qualitative free-text feedback that focused on participant familiarity with ED functioning, valuation of interprofessional collaboration before and after playing, and feedback on game usability and effectiveness. Recruitment was open to students in all health care and allied health professional programs at the institution. Forty-five participants were recruited from medical doctor, nursing, physiotherapy, and speech language pathology programs. ExpandED enhances participants' understanding of ED workflow (p < 0.001) and provides an enjoyable playing experience. However, participants' valuation of interdisciplinary teamwork did not change significantly before and after game play (p = 0.17). Participants expressed satisfaction with the game's accuracy in simulating the ED environment and appreciated the opportunity to collaborate with peers from different disciplines. Challenges reported included some tension among players, potential biases, and limitations of fidelity to a real-life ED. While this study has limitations regarding participant sampling and duration of gameplay sessions, it highlights the potential of ExpandED for teaching interprofessional collaboration in the ED. These findings will guide further development to optimize the expansion pack's effectiveness and its implementation into health care curricula.