Simulation is increasingly used in occupational therapy education with the objectives of developing practice skill competency and enhancing clinical reasoning. Debriefing, an integral part of the simulation process, is critical to achieving these objectives. This study sought to determine the types of debrief feedback Master of Science in Occupational Therapy (MScOT) students perceived as most useful and why, and how the advocacy inquiry model of debriefing influenced self-reported increases in clinical reasoning, client care, and planned implementation of feedback in practice. Using an embedded mixed method design with secondary data analysis, sixty-three first-year MScOT students provided 357 descriptions of the most useful feedback they received during 10-minute, facilitator-led debrief sessions after six simulations. Qualitative analysis revealed useful feedback was related to specific skills, interviewing and communication, the process of practice, strengths and encouragement, and client-centeredness. The advocacy inquiry approach was a useful delivery method of feedback. Logistic regression indicated that reported use of the advocacy inquiry model increased the likelihood by 4.7 times that students reported the debrief facilitated clinical reasoning. When advocacy inquiry was used in conjunction with providing feedback on specific skills, students were 5.3 times more likely to report planned implementation of the feedback in practice. Students value a variety of types of feedback during simulation debriefs. Debriefs using the advocacy inquiry method may be particularly useful for facilitating the development of clinical reasoning in the context of simulation-based fieldwork education.