Bullying usually involves an older or larger child (or several children) victimizing a single child who is incapable of defending himself or herself. Although much bullying goes unreported, it is estimated that in the average school an incident of bullying occurs approximately once every seven minutes. Bullying occurs at about the same rate regardless of class size or school size, but, for an unknown reason, rural schools appear to have a higher rate of bullying than urban or suburban schools. Even when bullying is reported, it is not always taken seriously by teachers and parents because many adults believe that children should learn to "stand up for themselves" or "fight back."

Although the stereotypical bully is male, girls engage in bullying behavior almost as often as boys. Their tactics differ, however, in that they are less visible. Boy bullies tend to resort to one-on-one physical aggression, while girls tend to bully as a group through social exclusion and the spreading of rumors. Girls who would never bully individually will often take part in group bullying activities such as "slam books," notebooks that are circulated among the peer group in which comments and criticisms are written about particular individuals.

Bullying begins at a very early age; it is not uncommon to find bullies in preschool classrooms. Up until about age seven, bullies appear to choose their victims at random. After that, they single out specific children to torment on a regular basis. Nearly twice as much bullying goes on in grades two to four as in grades six to eight, and, as bullies grow older, they use less physical abuse and more verbal abuse.

Until about sixth grade, bullies are not necessarily unpopular. They average two or three friends, and other children seem to admire them for their physical toughness. By high school, however, their social acceptance has diminished to the point that their only "friends" are other bullies. Despite their unpopularity, bullies have relatively high self-esteem. Perhaps this is because they process social information inaccurately.

For example, bullies attribute hostile intentions to people around them and therefore perceive provocation where it does not exist. "What are you staring at?" is a common opening line of bullies. For the bully, these perceived slights serve as justification for aggressive behavior.

In general, children who become the targets of bullies have a negative view of violence and go out of their way to avoid conflict. They tend to be "loners" who exhibit signs of vulnerability before being singled out by a bully. Being victimized leads these children—who are already lacking in self-esteem—to feel more anxious and thereby increase their vulnerability to further victimization. Being the target of a bully leads to social isolation and rejection by peers, and victims tend to internalize others' negative views, further eroding their self-esteem. Although bullying actually lessens during adolescence, that is the period when peer rejection is most painful for victims. In a number of well-publicized cases (in Scandinavia, Japan, and Australia, as well as the United States), adolescents tormented by bullies have been driven to suicide.

Evidence indicates that bullying is not a phase a child will outgrow. In a long-term study of more than 500 children, University of Michigan researchers discovered that children who were viewed as the most aggressive by their peers at age eight grew up to commit more (and more serious) crimes as adults. Other studies indicate that, as adults, bullies are far more likely to abuse their spouses and children.