Hybrid Effectiveness-Implementation Trial of an Executive Functioning Intervention for Children's Mental Health Services - PROJECT SUMMARY Autism is a highly prevalent neurodevelopmental condition, affecting 1 in 36 youth. The annual cost in the U.S. of autism was $223 billion in 2020 and is estimated to rise to $589 billion by 2030. Outcomes are poor and care disparities and high rates of unmet service needs are common. Mental health services play a key role in caring for autistic youth. There have been efforts to develop evidence-based interventions (EBIs) with the potential to lessen the public health burden of autism. Yet, research indicates limited community EBI penetration. Several gaps in work to date remain, including a focus on EBIs designed for community implementation and those addressing multilevel barriers impeding EBI use. There is an urgent need to focus on EBIs that improve mental health services for autism and optimize outcomes for this priority, complex population. Executive functioning (EF) is a potent mechanism underlying autism and commonly co-occurring mental health conditions. EF impairments (e.g., inflexibility, poor goal setting, poor planning) contribute to negative outcomes spanning multiple areas (e.g., academic, vocational, health). Our work underscores the impact of EF deficits on mental health services, including its transdiagnostic impact on the majority of children served in this setting and its role as a barrier to psychotherapy engagement and progress. EF is responsive to treatment, and mental health therapists cite a significant need and motivation for EF treatments, making EF EBIs highly relevant for community mental health settings. However, EF EBIs have not been widely used and tested in such settings. Autism EBIs, or those developed or adapted for autistic youth, have the potential to enhance mental health services, in addition to improving service quality for the populations targeted (e.g., autism). This is due to the specific components and strategies incorporated into the EBI to enhance its impact and fit. We propose a Hybrid Type 2 randomized trial examining the effectiveness and implementation of an autism EF EBI (Unstuck and On Target) in community mental health settings. Unstuck and On Target is a cognitive-behavioral EF intervention effective for autism. With NIMH funding (K23MH115100;), Unstuck and On Target was systematically adapted for and tested in mental health settings, with a pilot test suggesting its preliminary effectiveness, high fidelity, and use beyond autism. Findings have the potential to transform implementation and service quality for the high priority population of autistic youth as well as youth generally. Aim 1. Evaluate the effectiveness and implementation of an autism EBI (Unstuck and On Target), relative to a non-autism transdiagnostic intervention (Unified Protocol for Children) for autistic youth. Aim 2. Evaluate mediators of EBI training effects to confirm engaged change mechanisms of clinical and implementation outcomes. Aim 3. Explore the generalized effects of EBI training on reach and improved psychotherapy quality with non-autistic youth.