MIAMI • Nearly one in four US children suffers from chronic bullying at school, a problem that may lead to poor academic performance and low confidence over time, according to a recent study.

The findings in the Journal Of Educational Psychology are based on a study of 383 children who were followed from kindergarten through high school.

"It's extremely disturbing how many children felt bullied at school," said lead author Gary Ladd, a psychology professor at Arizona State University, who described the work as the first long-term bullying study of its kind. "For teachers and parents, it's important to know that victimisation tends to decline as kids get older, but some children never stop suffering from bullying during their school years."

Contrary to popular belief that bullying is prominent among older kids, researchers found that bullying was "more severe and frequent in elementary school and tended to taper off for most students as they got older", said the report.

"However, 24 per cent of the children in the study suffered chronic bullying throughout their school years, which was consistently related to lower academic achievement and less engagement in school."

Researchers gave annual surveys to the children and asked them to describe their experiences with bullying by other kids.

Similar findings were seen in children who had experienced moderate bullying that increased as the years went on, or about 18 per cent of the group. Fewer academic problems were seen among those who suffered less bullying as time went on, about 26 per cent of the group, suggesting that kids could recover if the victimisation stopped.

"Some kids are able to escape victimisation, and it looks like their school engagement and achievement does tend to recover," Professor Ladd said. "That's a very hopeful message."

Boys were significantly more likely than girls to be chronically bullied. About 32 per cent of children said they had experienced little or no bullying.

Prof Ladd urged parents to take action if they see their children struggling and said all schools should have anti-bullying programmes in place. "There has been a lot of consciousness raising and stories of children being bullied and committing suicide, and that has raised public concern," he said.

"But more needs to be done to ensure that children aren't bullied, especially for kids who suffer in silence from chronic bullying throughout their school years."

AGENCE FRANCE-PRESSE