Schools are a promising access point for youth with mental health concerns, but school-based mental health professionals (SPs) often need ongoing support to provide high-fidelity cognitive behavioral therapy (CBT). Adherence and competence, two critical elements of fidelity, were examined in a cluster-randomized implementation trial. We evaluated CBT adherence and then triangulated CBT adherence with end-of-study competence. We then evaluated the effects of two implementation supports, Coaching and (for slower-responding schools) Facilitation, on adherence and competence. By the end of the 43-week study period, 27.8% of SPs met adherence criteria. Adherent SPs scored higher on the competence measure, the CBT Competence Scale (t (116.2) = 3.71, p < .001). No significant difference in adherence was found among SPs at schools assigned to Coaching vs. not (Δ = 6.0%, p = .385), however SPs at schools randomized to Coaching scored significantly higher on two of the four competence subscales (Non-Behavioral and Behavioral skills). Among slower-responder schools, SPs at schools assigned to Facilitation were more likely to demonstrate adherence (Δ = 16.3%, p = .022), but there was no effect of Facilitation on competence. Approximately one quarter of SPs met adherence criteria in the trial; adequate delivery of exposure was a primary obstacle to reaching adherence. Facilitation may be especially suited to help SPs overcome barriers to delivery, whereas Coaching may be especially suited to help SPs improve CBT competence. Both are likely needed to build a mental health work force with the competence and ability to deliver EBPs in schools.