Bullying is an unwanted, aggressive behavior mostly among school aged children that involves a real power imbalance. The behavior is repeated, or has the potential to be repeated, over time. Both kids who are bullied and who bully others may have some serious lasting effects. Kids who bully abuse their power physically, embarrassing others publicly, or use their popularity—to control or harm others. Power imbalances can change over time and in different situations, even if they involve the same people.