Some children are bullies. They insult and abuse other children, lie to get them into trouble, start fights with them, and take their possessions without asking. There is much concern about the emotional and physical well-being of the bullies’ victims, the targets of their aggression. Although less attention has been paid to the effects on the bullies themselves, their social development may be harmed even more.

The causes of bullying probably include genetic, constitutional, physiological and social factors. But bullying often persists because it is immediately and substantially rewarded. By hurting others, bullies get what they want – high status, material possessions and self-esteem. As a result, aggression may be adopted as a way of solving problems very early in life and fully incorporated into a person’s response repertoire or personality by the middle of childhood. Any child who is aggressive in one situation is probably aggressive in most other situations. Physically aggressive children and adults are also likely to be verbally aggressive and to engage in other forms of anti-social behavior.

In a long-term study of 850 subjects, my colleagues and I found that an aggressive boy of 8 was likely to be an aggressive adolescent at 13 and an aggressive adult at 30. School bullying predicted serious anti-social behavior in late adolescence and adulthood. The records of adult men who had been aggressive as boys showed more criminal convictions for more severe crimes as well as more traffic violations and convictions for drunk driving. One out of every four highly aggressive 8-year-old boys had a criminal record by age 30; among other boys, the proportion was 1 in 20. Bullies also had fewer years of education and earned less money as adults than children who were not aggressive, regardless of the IQ and the social and economic status of their families.

Both men and women who had been aggressive children also tended to abuse their own children, often producing a new generation of aggressive children. In other respects, consistency over the years was less obvious in women than in men. In fact, the only adult characteristic that distinguished highly aggressive girls was the severity of the punishment they inflicted on their children. When these women were children themselves, physically aggressive girls were disdained. The same social circumstances may explain their harsh punishment of their own children: home is the one place where a woman can be physically aggressive without being seen and condemned.

One lesson for parents is that they should not encourage aggression by condoning violence in sports, teaching children that aggression is a good way to avoid attack, urging them to hit harder if they are hit, or justifying fights with the cliché "boys will be boys." Even more important is the example set for children by people in authority, heroes, and other children they admire. Observation and imitation are the most powerful learning mechanisms for young children.

Apart from parents and other children, the main source for models of violent behavior today is television. Children learn to imitate what they see on television, especially if they admire and identify with the actor or the character played by the actor. If a child is constantly exposed to television and film heroes who solve problems and win approval by aggression, the child will learn that aggression is effective. Television also influences a child’s understanding of how the world works, what behavior is appropriate in various situations, and how others can be expected to behave. This can provide a basis for self-justification by adults who persist in aggressive habits learned in childhood.