Previous research suggests that lower socioeconomic status (SES) adolescents bully more than their higher-SES peers. This paper tests whether aggression-related mindsets, defined as mindsets that theoretically influence aggressive behavior, explain the relationship between SES and bullying engagement among adolescents. Using a large and diverse dataset of survey responses from secondary students in the U.S. (N = 146,044 students, 30% White, 70% students of color from 5th-12th grade), this study applies structural regression modeling with complex survey data analysis. Results suggest that differences in aggression-related mindsets, including feelings of academic efficacy, feelings of purpose, global self-esteem, academic-status insecurity, school-related anger, and school-related happiness account for almost half of the relationship between SES and bullying. Students' school-related anger is the strongest direct predictor of bullying (0.88 standard deviation), which suggests that strategies to reduce adolescent bullying are more effective if they teach anger-reducing skills or eliminate the root causes of students' school-related anger.