Project Summary/Abstract Maltreatment prevention programs can promote public health by building protective factors among at-risk families. To maximize their benefits, programs should be delivered as intended by maintaining fidelity. Participant responsiveness (PR) is an under-studied fidelity construct defined as the degree to which participants “respond to or are engaged by” intervention at the behavioral, attitudinal, and relational levels. However, previous studies mostly focus on behavioral and attitudinal responsiveness such as attendance, follow-through, and satisfaction. The purpose of this study is to examine the role of participant Relational Responsiveness (RR) as a mechanism to increase protective factors against child maltreatment among the caregivers participating in the Family Success Network (FSN). The FSN is a community-based maltreatment prevention program piloted to serve 3 under-served counties in Ohio with high maltreatment rates. In FSN, coaches and families collaboratively develop a tailored plan of services designed to increase family protective factors. Focusing on primary and secondary prevention, FSN serves families with no history of substantiated maltreatment. Leveraging a Randomized Controlled Trial (RCT) funded by the Children’s Bureau, the proposed study will pursue the following aims; 1) To examine the structural validity of the Relational Responsiveness (RR) measure among FSN participants; 2) To determine the degree to which RR mediates FSN effects and whether RR’s mediation effects are moderated by caregiver race and gender; 3) To identify contexts within which RR’s mediation effects are activated or inhibited using a realist informed mixed-method approach. The accompanying training goals include developing competence in conducting 1) rigorous experimental studies examining implementation outcomes and program effectiveness; 2) mechanistic research using a realist-informed mixed-method design; 3) stakeholder-engaged research. The training and research will be overseen by Dr. Johnson-Motoyama, a professor in the College of Social Work at the Ohio State University (primary mentor). The results from this study will support a proposal for an R21/RO1 type II hybrid implementation and effectiveness trial in which I will engage stakeholders to develop and text tailored implementation strategies targeting RR.