Background: To support student mental health, school staff must have knowledge of evidence-based practices and the capacity to implement them. One approach used to address this challenge is a group-based telementoring model called "Extension for Community Healthcare Outcomes" (ECHO). In other applications (e.g., healthcare settings), ECHO has been shown to increase healthcare professionals' self-efficacy and knowledge of evidence-based practices leading to improved patient outcomes. Objectives: This study examined the potential for ECHO to be used as a method for increasing school staff engagement and knowledge of evidence-based school mental health practices. Methods: Using a quasi-experimental design, this study compared outcomes across two professional development experiences aimed at promoting school staff ability to provide evidence-based mental health services. School staff from four school districts participated in a school mental health training initiative. All participants (N = 57) had access to asynchronous, online mental health modules. A sub-sample (n = 33) was also offered monthly ECHO sessions. Results: Tests of group difference in outcomes revealed significant increases in engagement with online learning (d = 0.58) and satisfaction (d = 0.82) for those who participated in ECHO as compared to those who did not. Knowledge about evidence-based practices was not significantly different between groups. Conclusions: Results suggest that group-based telementoring may be a promising approach for improving engagement and satisfaction with training initiatives aimed at promoting evidence-based school mental health practices. However, further study of ProjectECHO using experimental designs is needed to make causal inferences about its effect on provider outcomes.