Children with medical complexity (CMC) are a growing population, yet training in complex care varies across pediatric residency programs. The purpose of this study was 1) to evaluate the effectiveness of a curriculum for pediatric residents in improving performance in a simulated clinical scenario; and 2) to explore residents' perceived self-efficacy in caring for CMC.A randomized controlled trial was conducted supplemented by qualitative inquiry. Pediatric residents from two residency programs were randomly assigned to participate in interactive modules on: (a) clinical assessment, care planning and technological dependency or (b) non-complex care topics. The primary outcome was mean score on an Observed Structured Clinical Examination (OSCE) of tracheostomy care. Semi-structured interviews were conducted post-intervention and analyzed using qualitative content analysis.Ninety-four eligible residents were randomized. Residents who attended all modules and the OSCE and consented to participate [intervention (n=20) and control (n=24)] were included in the final analysis. At baseline, few (9%) reported being comfortable caring for CMC. There was no significant difference in mean OSCE score between intervention and control groups (39.0±1.1 vs. 38.0±1.0, p=0.48). Qualitative analysis revealed three emerging themes related to resident self-efficacy: building a system of care, navigating uncertainty and professional identity formation.A standardized complex care curriculum delivered in a classroom setting did not lead to improved performance in an OSCE station despite increased resident-reported self-efficacy in approaching care for CMC. These findings highlight the need for multidimensional educational interventions and assessments in complex care.