Introduction: Emergency medicine (EM) practitioners must be proficient at caring for patients of all ages, including pediatric patients. Traditionally, EM trainees learn pediatric emergency medicine (PEM) through block rotations. This is problematic due to the seasonal nature of pediatric diseases and infrequent critical events. Spaced repetition learning theory suggests PEM would be better learned through longitudinal rotations. The transition to competency-based medical education (CBME) in Canada is accelerating the need to find novel ways to attain competencies in postgraduate training. At McMaster University, senior EM trainees can choose either traditional PEM blocks or longitudinal rotations. Our objective was to understand how learners experience these different rotations given the transition to CBME in Canada. Methods: Using a realist framework of program evaluation, we conducted semistructured interviews with key stakeholders (trainees, program directors, attending physicians) in EM. The realist framework was used to understand how context interacts with theoretical mechanisms to produce outcomes of interest. Data were analyzed using inductive, conventional content analysis. All investigators coded a subset of transcripts independently and in duplicate to achieve intercoder agreement.Results: A total of 13 interviews were completed with trainees (n = 11) and staff physicians (n = 2). The learning experience exists within an educational and clinical context, which are logistically distinct but inseparable. The longitudinal learning experience appears to improve learning through spaced repetition, which prevents atrophy of skills and knowledge while also benefitting from the offsetting of seasonal variability associated with many pediatric diseases. Improved feedback and entrustment are facilitated through the building of coaching relationships over time. Barriers to the learning experience are related mainly to logistical difficulties associated with resolving longitudinal and blocked learning experiences. Improved relationships with the interprofessional team may provide distinct learning opportunities and improved team functioning. Block rotations were identified as more valuable to junior trainees learning fundamental concepts.