PROJECT SUMMARY/ABSTRACT Many evidence-based preventative interventions have been developed to prevent substance use, physical and mental illness, and promote positive educational and social outcomes among adolescents. Among these, caregiver-mediated interventions boast strong effects that are mediated by effective parenting skills. However, the impact of these interventions is severely limited by low rates of home practice of intervention skills among caregivers. To address this research-to-practice gap, researchers have been investigating barriers and facilitators of caregiver engagement, focusing in large part on intervention attendance. Strategies for increasing caregivers' home practice of skills remain underexamined. Yet, caregiver home practice is a key component of theorized intervention effectiveness and has been found to impact parenting behaviors and subsequent child outcomes over and above that of attendance. Therefore, the next important step in supporting parenting behavior change is to develop implementation support strategies for evidence-based interventions that target caregiver home practice specifically. This proposed K01 Mentored Research Scientist Development Award will develop and pilot a digital behavior change intervention for use as an adjunct to an evidence-based preventative intervention. The “Modular Engagement and Skills Augmentation” (MESA) aims to increase caregivers' home practice of intervention skills. Informed by the theory of planned behavior, habit formation principles, and relapse prevention theory, MESA will leverage mobile health technologies (mHealth) to circumvent and problem solve common barriers to home practice including home practice intention, frequency of practice, home practice competence, and maintenance of intervention skills. MESA will be developed as a smartphone application (i.e., “app”). MESA components will be informed by a qualitative assessment of barriers to caregiver home practice and refined through direct stakeholder input on design requirements to optimize acceptability and feasibility. MESA will be piloted with 48 caregiver participants as an adjunct to Bridges, an evidence-based intervention for adolescent substance use prevention and mental health promotion. Cluster randomized controlled design will be utilized such that Bridges intervention groups will be randomly assigned to receive MESA (n = 32) or an active control (n = 16). Findings from this study have the potential to improve caregiver home practice, intervention engagement broadly, and ultimately boost effectiveness and public health impact of numerous caregiver- mediated interventions.