PROJECT SUMMARY — SIGNATURE PROJECT (SP) Community-based pediatric primary care offers a tight net for identifying children experiencing mental health disparities who would benefit from preventive services and support. Parenting-based interventions are effective at reducing risk for common mental health problems in toddlers but have not been translated to primary care. Embedding evidence-based programs in existing systems of care reduces the likelihood of mental health prob- lems emerging. A challenge of widescale prevention efforts in primary care is systematic, unbiased methods for identifying children at risk for mental health problems. Salient factors limiting equitable implementation of screen- ing practices and linked parenting interventions are feasible and acceptable risk identification processes, the cost of implementing these practices, and the need for a well-trained workforce, strategies to engage caregivers, and accessible delivery solutions. The MHE Center's Signature Project (SP) proposes a linked mental health risk calculator to identify toddlers, the Developmental Early Childhood Instrument for Deciding Equitably for Men- tal Health (DECIDE4Mental Health) tool, and a telehealth and digital application-based version of the evidence- based Family Check-Up® (FCU), called FCUOnline, that has demonstrated effects on parenting and child self- regulation that leads to short- and long-term prevention of internalizing and externalizing problems. The SP will be the first implementation of FCUOnline in safety-net primary care agencies with predominantly Black/African American and Latino low-income families in an urban area. Our transdiagnostic decision tool is key to develop- mentally reliable mental health risk determination that is feasible in routine care, because they identify risk for a broad array of syndromes with a single screen. Using the MHE Center's novel cluster randomized Roll-Out Implementation Optimization (ROIO) design, the SP's aims are: Aim 1: Optimize the implementation of DE- CIDE4Mental Health in pediatric primary care linked to an evidence-based telehealth parenting interven- tion—the Family Check-Up® (FCU) Online. Aim 1a. Identify and test strategies for equitable implementation of DECIDE4Mental Health tool. Aim 1b. Identify and test strategies for equitable implementation and effectiveness of the FCUOnline. The SP's implementation optimization process and outcome evaluation are guided by the RE- AIM framework with a focus on equitable implementation. Aim 2. Evaluate the equitable implementation of DECIDE4Mental Health and FCUOnline. We will assess equitable implementation of the SP's tools on key clinic, clinician, and caregiver levels implementation outcomes at multiple points within the ROIO design to opti- mize strategies directed at any signs of inequity. Aim 3. Test the effectiveness of FCUOnline at reducing toddler behavioral vulnerability to preschool-age mental health symptoms. Experimental Therapeutic target...