"An Individualized Mental Health Intervention for ASD" (AIM HI) was developed in collaboration with community stakeholders for delivery in mental health services in response to therapist- and caregiver-identified need to improve services for children with autism spectrum disorder (ASD). Primary findings from a cluster randomized Hybrid Type 1 effectiveness-implementation trial conducted in publicly funded mental health programs demonstrated the effectiveness of AIM HI therapist training on child and caregiver outcomes. This study examined therapist outcomes and therapist experience as a moderator of training effects. Mental health programs were randomized to immediate AIM HI training or usual care. Therapists and child/caregiver clients were recruited from participating programs. Therapists in the AIM HI training condition received consultation for 6 months while delivering AIM HI. Differences between training conditions were examined using multilevel modeling. Therapists receiving AIM HI training were observed to use more extensive active teaching strategies with caregivers, engagement strategies with children, strategies promoting continuity of care, and had more structured sessions with more extensively pursued skill building. Therapist licensure moderated some training outcomes. The current study provides support for evidence-based practice implementation in usual care mental health services.