School staff increasingly seek to implement evidence-based school mental health services to promote student mental health. However, barriers to accessing programming and support mean that implementing these programs is difficult. Popular strategies to address these challenges, like one time professional development, often fail to be effective or sustainable. This study used mixed methods to evaluate how a set of training activities--sequential online learning modules combined with interprofessional telementoring, following the extension for community healthcare outcomes (ECHO) model--influenced provision of school mental health services. School counselors, nurses, psychologists, and social workers (n = 46) participated in training activities, which included nine, cohort-based ECHO sessions and 12 modules. We used a concurrent mixed methods design in which quantitative (implementation data and pre-post surveys) and qualitative (posttraining focus groups with a subset of participants, n = 11) data were used to evaluate training. Quantitative results indicated statistically significant pre-post improvements in participants' clinical self-efficacy (d = 0.83) and knowledge of evidence-based practices (d = 0.37). Qualitative data corroborated quantitative results. Post training, focus groups described positive reactions, learning, and behavior change, particularly with respect to equitable service provision and interprofessional teaming. ECHO appeared to facilitate the application of evidence-based strategies to real-life practice and improved participants' understanding of effective coordination of services. Taken together, findings suggest that group-based telementoring may be a high-impact strategy for supporting the implementation of effective, culturally specific, and collaborative school mental health services.