7. PROJECT SUMMARY/ABSTRACT Bullying is defined as intentional aggressive behavior that typically occurs repeatedly over time in the context of a power differential.1,2 It is a public health concern3,4 because of its high prevalence and the deleterious impacts on children’s social-emotional wellbeing, academic achievement, and health.5-8 In the school setting, bullying can be inadvertently condoned through teacher non-response or ineffective responses to aggressive and bullying behaviors.9-11 Teachers play a pivotal role during late childhood (i.e., elementary school) because students are often with the same teacher most of the day, allowing for more opportunities to shape their social development.12 Late childhood is also a key developmental period when bullying increases and shifts to more covert behaviors that are difficult for teachers to detect.13-15 Though there are widespread mandates to address bullying in schools16, programming is often aimed at students’ behaviors or brief professional development (PD) for teachers. These PDs do not focus specifically on key knowledge, attitudes, and skills related to the specific role that school staff play in creating a positive social emotional climate through behavior management and preventing and intervening with bullying. Therefore, to address these critical gaps in bullying prevention programming our team developed and piloted the Bullying Classroom Check-Up (BCCU).17-19 The BCCU enhances bullying prevention programming beyond the typical student-focused approach. It is an innovative, collaborative, and data-informed bullying prevention model that includes group-based professional development for all school staff and one-on-one coaching that rigorously supports classroom teachers in preventing, detecting, and intervening with bullying behaviors. The BCCU incorporates one-on-one coaching using an adapted version of the Classroom Check-Up20, which leverages motivational interviewing to empower teacher practice changes, as well as the mixed-reality TeachLivE© simulator21, and PD Modules. The BCCU was tested in a 78 teacher, classroom- randomized trial within 5 middle schools (NIJ grant: 2015-CK-BX-0008) and demonstrated improved teacher attitudes and skills in bullying detection and intervention.17 To avoid prior design challenges and prevent contamination, this study will utilize a more rigorous school-level, cluster randomized controlled trial.22 This 32 elementary school trial, conducted in the Baltimore metro area and Philadelphia across 5 years, will examine BCCU effects on 3rd to 5th grade students’ reports of bullying prevalence (i.e., perpetration, victimization, and witnessing) as well as the general bullying climate, sense of safety, and positive bystander responses both at post-test and in the next school year. We will also examine the effects of the BCCU on teacher skills/efficacy as well student-teacher and student-student relationships across two school years. Finally, we will explore ...