Educators have embraced the promotion of social emotional development, student well-being, and mental health as essential educational objectives to promote academic readiness and growth. To address known research-to-practice gaps and limited availability of evidence-based, universal high school programs, we took a community-based participatory research (CBPR) approach to develop a contextually and developmentally appropriate program addressing social emotional learning, community, and student well-being. We employed the ADDIE (Analyze, Design, Develop, Implement, Evaluate) model of systematic instructional design for two school years. We collected quarterly anonymous open- and close-ended surveys from students and teachers and open-ended session-specific surveys from teachers; led student advisory and teacher focus groups; and documented coach feedback and observations. Researchers conducted qualitative descriptive and quantitative descriptive analyses. We summarize how CBPR and the ADDIE model of systematic instructional design was applied to ensure contextual fit and acceptability in high schools. We present how findings from the data sources were used to design and develop content and highlight results on comfort, content of interest, and optimal time dedicated to content. We describe how we developed the components of Well Connected©. We conclude with lessons learned for co-developing programs and engaging in participatory research. [This paper was published in "School Mental Health" v16 n3 p846-861 2024.]