Developing a bullying prevention program that transcends physical boundaries - An estimated 20-24% of middle school students bully their peers ‘regularly’ or more often each semester. Bullying involvement is associated with externalizing problems (e.g., alcohol use) for bullies and internalizing behaviors (e.g., depressive symptomatology), and suicidal ideation and behavior for victims. Efforts to reduce bullying perpetration, thereby also reducing victimization, are critical. Existing bullying prevention programs have only a modest impact in elementary school settings and even less of an impact in middle schools. Approaches that avoid adult involvement and integrate less proscriptive language may have more impact on behavior change. We believe text messaging is one such approach as it provides novel opportunities to “go where youth are”: Nearly all (91%) of the nine in ten teens who own cell phones use text messaging, and usage is high across race, income, and rural vs. urban settings. Content can be written to be approachable and not sound as if it is being delivered by an authority figure, Importantly, emerging evidence suggests that text messaging- based programs can affect behavior change. This R21 proposal is an extension of our development work with BullyDown, a text messaging-based bullying prevention program designed for middle school students. Guided by the Social-Emotional Learning (SEL) model, the intervention content and program features have been iteratively refined within ongoing feedback from middle school youth from across the country. The program was then beta tested with 22 middle school students in Illinois. Nine in 10 said they liked the program, and all intervention participants said that it equipped them with skills needed to not bully others in the future. Building upon our promising findings, we propose to further develop and then pilot test BullyDown in a randomized controlled trial (RCT) of middle school students. Specifically, we aim to: Specific Aim 1: Finalize the BullyDown program. Feedback from beta test participants will be integrated into the intervention. We also will update program content to acknowledge the growing infusion of technology in the classroom, and the online interactions that it requires. To do so, we will first conduct focus groups to understand how young people are interacting with each other online in academic settings. Then the updated content will be reviewed by Content Advisory Teams to ensure that it is understandable and salient. Specific Aim 2: Pilot test the 7-week BullyDown intervention for feasibility and acceptability in an RCT of 150 middle school students. Youth will be randomly assigned to either BullyDown, a 4-message- per-day program, or an attention-matched control group talking about ‘healthy lifestyle’ topics (e.g., exercise). Our main outcome measures will be feasibility (e.g., retention rates) and acceptability (e.g., positive program appraisal). Behavioral outcomes will inform power analyses, and include bullying perpetration.