Existing research into learning about patient safety focuses on identifying how educational interventions improve educational outcomes but few studies offer evidence that inform educators about the mechanisms involved in learning about patient safety. The current evidence based in undergraduates is also limited to outcomes that relate to knowledge and skills. A realist approach involving three cycles of data collection in a single cohort of students over 5 years used different outcomes in Kirkpatrick's framework to identify the mechanisms that influence students learning about patient safety. Data source 1. Focus groups identified an overarching theoretical model of the mechanisms that influence patient safety learning for medical students. Data source 2 Identified if the mechanisms from data source 1 could be demonstrated at the outcome level of knowledge and attitudes. Data source 3 Established associations between mechanisms and outcomes at skills and behavioural level, in a standardised simulated ward setting. Data source 1: The interpretation of data from seven focus groups involving sixty students identified reflection at two levels of Mezirow's descriptions; reflection and critical reflection as mechanisms that influence learning about error. Data source 2: Sixty-one students participated. The associations found, reflection and knowledge of actions to take for patient safety, r = 0.44 (P = 0.00) and critical reflection and intentions regarding patient safety, r = 0.40 (P = 0.00) Data source 3: Forty-eight students participated. The correlation identified associations between critical reflection and planned changes following feedback was, r = 0.48 (P = 0.00) and reflection and knowledge based errors r = -0.30 (P = 0.03). A realist approach identified two different levels of reflection were associated with different patient safety outcomes for this cohort of students. Critical reflection was associated with attitudes and reflection was associated with knowledge of actions and error behaviours. These findings give educators greater depth of information about the role of reflection in patient safety.