While social emotional learning (SEL) school-based initiatives can benefit student well-being and learning, a need remains for a more nuanced understanding of aspects affecting systemic SEL integration within under-resourced learning environments. This study considered factors affecting implementation of a community initiative to provide schoolwide SEL curriculum and mental health support services at an economically disadvantaged school district in the USA at a time when students were returning to fully in-person learning after the COVID-19 pandemic lockdown. School administrators, counselors, teachers, SEL coaches, and mental health professionals (n = 23) participated in individual interviews or focus groups to discuss their experiences implementing schoolwide SEL services during this time. Results from reflexive thematic analysis indicated themes around facilitators and barriers to maintaining systemic SEL in the school district. Facilitators to schoolwide SEL implementation included faculty and staff efforts to normalize talk about mental health and collaborate when providing SEL content and mental health support. Implementation barriers included insufficient professional staffing, student absenteeism, and teacher and student resistance to SEL. Findings underscore the need for future research to examine the feasibility and effectiveness of differing collaborative approaches to SEL implementation as well as methods for addressing low teacher/student SEL responsiveness to mental health programs in underserved schools. Interventions should also consider ways to proactively address challenges to schoolwide SEL implementation in lower-income communities, including decreased leadership support.