Autistic youth frequently experience interfering anxiety, and schools may be an ideal setting to deliver mental health care. A type 1 hybrid-effectiveness, cluster randomized trial was used to examine the effectiveness of school-based Facing Your Fears compared to usual care. Change in provider cognitive behavior therapy knowledge and treatment fidelity (adherence and provider competence) were also examined. Seventy-seven interdisciplinary school providers across 25 elementary/middle schools were trained via a train-the-trainer approach. Eighty-one students, ages 8-14 years, with autism or suspected autism and anxiety participated. Students who received school-based Facing Your Fears displayed significantly greater reductions in anxiety compared to students in usual care according to caregiver and child report (Screen for Anxiety and Related Emotional Disorders). Significant reductions in total anxiety (p = 0.012), separation (p = 0.002), and social anxiety (p = 0.003) subscales occurred, according to parent report. Student self-report indicated significant reductions on the social anxiety subscales (p = 0.001). Interdisciplinary school providers demonstrated significantly increased cognitive behavior therapy knowledge following training (p < 0.001). Mean adherence and competence ratings were strong. The positive effectiveness and implementation outcomes are encouraging. Training interdisciplinary school providers to deliver school-based Facing Your Fears has the potential to increase access to care for anxious autistic students. Future directions and limitations are discussed.