Bullying is a significant problem in the USA, with 1 in 5 middle school students reporting being a target of bullying. Although prevalence rates of bullying are higher among students in low-income communities and among minority students in ethnically blended schools, the majority of research on bullying prevention has been conducted with primarily White samples. Further, many available anti-bullying programs require significant resources for implementation, leading to barriers for schools in low-income communities. The purpose of this study was to examine the effectiveness of a brief, bystander preventive intervention (STAC) adapted to be culturally appropriate for students in ethnically blended schools in low-income communities. The STAC acronym stands for the four strategies students are taught to use to intervene in bullying behavior: "stealing the show," "turning it over," "accompanying others," and "coaching compassion." Participants were sixth grade students (N = 147) at an ethnically blended school in a low-income community. The social validity of the program was assessed through measures of program acceptability, student learning, and use of intervention strategies in bullying situations. Program outcomes included bullying behavior, depressive symptoms, and social anxiety. Results indicated that students trained in the adapted STAC program found the program to be acceptable, reported a significant increase in knowledge and confidence, and reported using the program strategies post-training. Students also reported a significant decrease in bullying behavior, depressive symptoms, and social anxiety. Findings suggest that the adapted STAC program is a promising approach for bullying prevention for ethnically blended middle schools in low-income communities.