Background: School-based programs are widely implemented to address childhood obesity. Despite the promise of these programs, evidence on their effectiveness is mixed. Adopting a dissemination and implementation (D&I) science focus utilizing mixed methods can provide a broader understanding and more robust details about these programs. The goal of this evaluation is to understand how implementation factors and teacher experience influence implementation success and outcomes of the Integrated Nutrition Education Program (INEP), an elementary school-based nutrition program, using a mixed-methods design. Methods: Reach, effectiveness, adoption, implementation, maintenance (RE-AIM) framework guided the development of the evaluation and multiple methods were deployed. Hierarchical linear regression was used to assess the association between D&I construct variables within levels of influence and teacher perception of INEP impact from a quantitative end-of-year teacher survey. Follow-up qualitative interviews with teachers were analyzed using constant comparison analysis. Results: Workload and burden emerged as significant factors related to implementation in the quantitative analysis. The follow-up qualitative data collection identified other factors teachers found important to the adoption, implementation, and maintenance of INEP. Conclusion: Results of this evaluation can be used to inform program improvement efforts for INEP and provide information on ways to promote reach, effectiveness, adoption, implementation, and maintenance of similar school-based health promotion programs.