Introduction: Educators have theorized that interventions grounded in dual process theory (DPT) and script theory (ST) may improve the diagnostic reasoning process of physicians but little empirical evidence exists. Methods: In this quasi-experimental study, we assessed the impact of a clinical reasoning (CR) curriculum grounded in DPT and ST on medicine residents participating in one of three groups during a 6-month period: no, partial, or full intervention. Residents completed the diagnostic thinking inventory (DTI) at baseline and 6 months. At 6 months, participants also completed a post-survey assessing application of concepts to cases. Results: There was a significant difference between groups in application of concepts (no intervention 1.6 (0.65) compared to partial 2.3 (0.81) and full 2.2 (0.91), p = 0.05), as well as describing cases in problem representation format (no intervention 1.2 (0.38) and partial 1.5 (0.55) compared to full 2.1 (0.93), p = 0.004). There was no significant difference in change in DTI scores (no intervention 7.0 (16.3), partial 8.8 (9.8), full 7.8 (12.0)). Conclusions: Residents who participated in a CR curriculum grounded in DPT and ST were effective in applying principles of CR in cases from their practice. To our knowledge, this is the first workplace-based CR educational intervention study showing differences in the reasoning process residents apply to patients.