Background <p>Influenza vaccination rates remain low among primary school students and vary by school, even under the free School-Located Influenza Vaccination (SLIV) in Beijing, China. To improve influenza vaccination coverage, we developed multifaceted, enhanced SLIV (E-SLIV) strategies in response to factors that influenced the SLIV implementation. The E-SLIV strategies were proved with modest effectiveness in improving influenza vaccination uptake via a cluster randomized trial in the 2022–2023 influenza season. This paper reports the implementation outcomes and identifies influencing factors for the implementation of the E-SLIV strategies, which was conducted in the same settings.</p> Method <p>The E-SLIV intervention study involved 20 primary schools in Beijing, China, which were randomly allocated in a 1:1 ratio to the intervention (i.e., E-SLIV) or control (i.e., usual SLIV practice) groups in the 2022–2023 influenza season. This study applied a convergent mixed methods design to evaluate implementation outcomes specifically for 10 schools in the E-SLIV group. Quantitative data were collected from 39 implementers via a close-ended questionnaire and a project-specific implementation checklist, and from 915 parents via a close-ended questionnaire. Qualitative data were gathered from 18 implementers and 8 parents via semi-structured interviews. Quantitative descriptive and qualitative thematic analysis were applied, with findings integrated via joint display for meta-inference based on an evaluation framework that combines the Reach, Effectiveness, Adoption, Implementation, Maintenance (RE-AIM) framework with Normalization Process Theory (NPT).</p> Results <p>E-SLIV reached 1,172 of the 1,541 targeted students in 10 intervention schools, representing an intervention coverage rate of 76.1% (95% CI [74.0%, 78.2%]). Qualitative findings indicated that the E-SLIV strategies may have limited success in reaching those with social media information overload and those who were hesitant about influenza vaccination. All 10 schools adopted the overarching E-SLIV strategies, but insufficient priority and endorsement from school administrators may have hindered the consistent adoption of specific program components. Both quantitative and qualitative findings suggested the E-SLIV strategies were flexible with adequate resources, enabling good implementation of most intervention components. However, relationships, skills, contexts, and content integration needed strengthening, and implementation was limited by COVID-19 related workload and vaccination uncertainty, and vaccine shortage, as the qualitative findings indicated. Around 83.3% (95% CI [73.4%, 93.2%]) of school implementers and 70.4% (95% CI [67.4%, 73.4%]) of parents favored maintaining E-SLIV.</p> Conclusion <p>The multifaceted E-SLIV strategies reached most target populations and were well-implemented with high fidelity by most schools. The E-SLIV strategies strengthened collaboration, enhanced capacity, and provided tailored education, yet faced challenges including entrenched parental views, social media information overload, inadequate school leadership, low proactivity among school doctors in coordinating vaccinations, the COVID-19 pandemic, and temporary vaccine shortages. Findings inform future optimization of school-based vaccination programs and present a compelling case for measuring implementation outcomes using mixed methods.</p>