Bullying is a "serious public health problem," and should no longer be dismissed as merely a matter of kids being kids, a leading panel of experts warned Tuesday.

"Its prevalence perpetuates its normalization. But bullying is not a normal part of childhood," the National Academies of Sciences, Engineering, and Medicine said.

Bullying behavior is seen as early as preschool and peaks during the middle school years, the researchers said. And the problem has morphed from the traditional bully-in-the-schoolyard scenario to newer forms of electronic aggression, such as cyberbullying on social media sites.

Bullying has "lasting negative consequences and cannot simply be ignored," said Frederic Rivara, chairman of the committee that wrote the report and a professor of pediatrics and epidemiology at the University of Washington.

"This is a pivotal time for bullying prevention, and while there is not a quick fix or one-size-fits-all solution, the evidence clearly supports preventive and interventional policy and practice," Rivara added.

The report said both bullies and their victims can suffer short and long-term consequences, including poor grades, anxiety and depression.

The Education Department has said that students who are bullied also are at a higher risk of suicide.

Zero-tolerance policies at school, in which students are automatically given suspensions for bullying, don't help reduce bullying and should be discontinued. Instead, the researchers said, schools should refocus resources on preventative intervention policies and programs, though it recommended more study on which programs work best.

The committee also concluded that zero-tolerance policies may lead to an underreporting of bullying — because the consequence of suspension is perceived as too harsh and punitive.

More on this...

A government report this month on school crime from the National Center for Education Statistics and the Justice Department suggested bullying is down sharply from more than a decade ago. It found the percentage of public schools reporting bullying at least once a week decreased from 29 percent in 1999-2000, to 16 percent in 2013-14.

The National Academies was more cautious about trying to gauge the extent to which bullying is a problem across the country. In its report, it said bullying likely affects between 18 percent and 31 percent of young people. It had lower estimates for cyberbullying victims, saying it ranged from about seven to 15 percent of youngsters.

The committee also looked at the relationship between bullying and school shootings, but concluded that the data are unclear on the role of bullying as a factor or cause in the shootings.