BackgroundMass casualty incident (MCI) triage simulation is an increasingly useful tool for teaching triage systems to medical students, trainees, and hospital staff. MCI simulation in the prehospital setting has not yet been studied in this population.Objectives/AimsWe aimed to assess the effectiveness of a prehospital MCI simulation in medical students, residents, and fellows. Our primary outcome was knowledge of the components of the triage algorithms used in MCI response. Our secondary outcome was each participant's confidence level if required to assist with or lead a MCI response.MethodsThis was an observational study with pre–post surveys. We recruited 30 medical students, 14 emergency medicine (EM) residents, and four pediatric EM fellows to fill out a survey before and after a 3‐h simulation session practicing the START and JumpSTART algorithms on two prehospital MCI scenarios.ResultsOverall, all groups demonstrated significant improvement in knowledge of triage colors, information needed to assign a triage color, pediatric airway management during a MCI, and indications for breaths‐first CPR. They also demonstrated significant increase in confidence both in assisting with and in leading a MCI response.ConclusionsSimulated practice triaging patients in prehospital MCI scenarios improves knowledge of triage algorithms and increases confidence in assisting with or leading a MCI response in medical trainees.