What Makes A Bully?

Bullying is on the rise among young people but the cause is unknown. This paper provides a first empirical study on the cause of bullying perpetration with a focus on the socioeconomic status inequality within the class. Using a sample of 7th-graders who were randomly assigned to classes at the beginning of middle school, I find that a 0.1 units increase in the within-class standard deviation of SES led to an increase in the average probability of becoming bullies by1.4 percentage points. The effect concentrate among the higher ability students, younger, male and less motivated students. Policy simulations suggest that reducing the within-class standard deviation of SES led to a reduction in the probability of bullying perpetration by 2.7 percentage points. It provides a solid ground for interventions to reduce bullying incidents.