Determining the factors that influence implementation of school-based wellbeing and health programs is essential for achieving desired program effects. Using a convergent mixed-methods, multiple informant design, this study considered factors that influence implementation of health programs for ninth grade students and in what ways implementation is differentially perceived by multiple informants (i.e., participants, instructors, and independent observers). Two types of programs--mindfulness and health education--were implemented with ninth graders (N = 70) in three schools situated in low-resourced urban neighborhoods. Study outcomes were derived from four data sources: (1) focus group participants (N = 45); (2) program instructor fidelity ratings; (3) independent observer fidelity ratings and notes; and (4) instructor open-ended session responses. Using thematic and mixed methods integration analyses, we identified themes related to implementation promoting or challenging factors. Theme names differed when data sources were separately analyzed by informant. Mixed methods integration analysis indicated that four themes were common across all informant groups: (1) competent, attentive, and engaging instructors are essential; (2) programs should involve interactive components (e.g., physical activities, applied learning opportunities); (3) adequate time for program delivery is key for student exposure and engagement; and (4) students' availability and preferences should guide program scheduling. A fifth theme, unique to instructor and observer perspectives, was that program implementation was negatively impacted by distractions from multiple sources, including instructors, students, and settings. Recommendations from students, instructors, and observers for implementation optimization are discussed.