Background: There is considerable evidence that physicians lack sufficient training in facilitating transition from pediatric to adult care systems for adolescents and young adults (A/YA). While several primary care residency programs have introduced health care transition (HCT) curricula in recent years, there are few studies that assess the effectiveness of HCT teaching models. Purpose: To assess the impact of a residency education program that uses electronic health records (EHR) and other methods to teach residents how to prepare A/YA for transition to adult care. Methods: In a mixed methods, quasi-experimental research design, quantitative methods were used to measure change in knowledge, confidence and experience among 67 Pediatrics and Med-Peds residents who participated in the program. All residents and a comparison group were invited to complete a 35-item pre/post-survey; a retrospective chart review provided documentation of age-specific HCT preparation tasks completed by residents during well visits for A/YA aged 12-21. Descriptive and correlational analyses were conducted to compare differences between resident and control test scores for 5 outcome variables, and to measure resident utilization of the HCT tool in the EHR. Using the Reach Effectiveness-Adoption Implementation Maintenance (RE-AIM) evaluation model as a guide, semi-structured interviews were conducted concurrently with residents and faculty to assess program acceptability, feasibility, and other important attributes. Interviews were transcribed and analyzed using a constant comparative, iterative process. Results: Survey results showed residents (11 matched pairs) scored significantly higher than controls (13 matched pairs) in 2 of 5 outcomes: exposure to HCT learning activities (p=.0005) and confidence in providing primary care for YSHCN (p=.0377). Overall utilization of the EHR tool among 51 residents was 52.8% (57 of 108 patient visits). In interviews conducted with 16 residents and 6 faculty, both groups said that HCT training is a highly relevant need. Residents said they had little knowledge or experience in HCT prior to the intervention but felt more confident in their abilities afterwards. The HCT tool in the EHR was the only intervention element among multiple modalities that reached all study participants, with more than 80% of residents interviewed reporting they used the HCT tool "usually" or "always." Factors that influenced program adoption included accessibility of educational materials, ease of use, time constraints, patient age and health condition, and attending physicians' enforcement of the protocol. Conclusion: This study contributes to the body of knowledge concerning HCT by increasing our understanding of ways to effectively educate residents about transition preparation. Results show a positive intervention effect on selected dimensions of resident knowledge, confidence, and practice in HCT, highlighting program strengths and weaknesses. The program is distinctive in educating residents to prepare all A/YA for HCT, as recommended by major medical associations for pediatric and adult care physicians, and in its use of the EHR as a primary teaching tool, a consideration for reducing time-intensive didactic instruction. It provides a model that can be adapted by other residency and provider training programs, and suggests a need to integrate acquisition of health care self-management skills more broadly in child and adolescent health preventive care tools and policies.