Background: Objective-structured teaching encounters (OSTEs) are used across many disciplines to assess teaching ability. The OSTE detailed in this paper assesses 191 fourth-year medical students’ (M4) ability to identify and address lapses in professionalism based on Association of American Medical Colleges’ professionalism competencies. The research questions addressed are: How frequently do M4s address professionalism lapses observed during an OSTE? What factors influence whether M4s provide feedback when they observe professionalism lapses in an OSTE? Methods: Standardized patients (SPs) and standardized learners (SLs) were recruited and trained to participate in a standardized encounter with specific cognitive, social, and behavio...