Amid growing concern over school violence, a nationwide study has found that bullying affects nearly one of every three U.S. children in sixth through 10th grades. Young students and boys were most likely to be affected.

The authors say their 1998 survey of 15,686 public and private school students is among the first to document the prevalence of bullying in U.S. classrooms, and the results show that not enough has been done to prevent what is often seen as an unpleasant rite of passage.

“It’s a problem that has been in a lot of ways ignored for quite a while,” said lead author and researcher Tonja Nansel of the National Institute of Child Health and Human Development.

The survey appeared in the April 25 Journal of the American Medical Association. It is part of the U.S. contribution to a study of worldwide childhood health and behavior by the World Health Organization.

Bullying has been implicated in recent school shootings, including the March slayings of two students in Santee, Calif., and the 1999 massacre of 13 by two suicidal students at Colorado’s Columbine High School.

Since nationwide research on bullying is so scarce, the survey doesn’t show whether the U.S. prevalence is rising, Nansel said.

Children who said they were bullied reported more loneliness and difficulty making friends, while those who did the bullying were more likely to have poor grades and to smoke and drink alcohol.

Other research has shown that people who were bullied as children are prone to depression and low self-esteem as adults, and that bullies are more likely to engage in criminal behavior.