Researchers said the findings shed light on some of the school shootings in recent years. Many such incidents involved young assailants who were said to the have been bullied.
"The implication is that children who bully other children may benefit from programs seeking to prevent not just bullying, but other violent behaviors," said Dr. Duane Alexander, director of the National Institute of Child Health and Human Development.
Institute researcher Tonja Nansel led the study, which was released Monday in April's Archives of Pediatrics & Adolescent Medicine.
While bullying victims in the study faced increased risks of engaging in more serious aggressive behavior, the highest risks were for bullies themselves, especially those who frequently bullied away from school.
They were more than five times more likely to carry weapons at or away from school than kids who did not engage in such behavior.
Dr. Howard Spivak, chairman of an American Academy of Pediatrics violence task force, said bullies "are waving major red flags that something's seriously wrong." He said bullies usually want an audience to further "empower" themselves — and those who do it without the possibility of a large audience could have an even greater problem.
The study involved a nationally representative group of 15,686 students in grades six through 10 who completed a World Health Organization survey in 1998.
Children were asked about the occurrence and frequency of bullying or being bullied; carrying weapons such as a gun, knife or club; physical fighting; and injuries from fights.
Overall, 30 percent of students reported occasional or frequent involvement as a victim and/or perpetrator in bullying, which was defined in the study as unwanted teasing or "nasty" verbal or physical behavior directed toward someone less powerful. Those results were reported two years ago.
The new data shows that nearly 23 percent of boys had carried a weapon outside of school and 15 percent had carried one in school in the past month. For girls, those figures were nearly 7 percent and 4 percent respectively.
Thirteen percent of boys and 6 percent of girls had been in four or more physical fights in the past year; and 23 percent of boys and 11 percent of girls had been injured in a fight in that time.
That translates to nearly 2 million students involved in frequent fighting and nearly 3 million injured in the past year nationwide, the researchers said.
Youngsters who were bullied weekly in school were 60 percent more likely to carry a weapon to school, 70 percent more likely to be in frequent fights and 30 percent more likely to be injured than those who weren't bullied.
Weekly school bullies were also three times more likely to carry a weapon in school and be involved in frequent fights, and twice as likely to be injured in fights as non-bullies.
Bullying is a problem that parents and community leaders, not just school officials, need to address, Nansel said.
"We certainly want our schools to be safe, but we can't stop there," she said.