Treating mental-health problems in children entering school may help prevent victimization from bullying, say researchers who tracked 400 Canadian children.

In the May/June issue of the journal Child Development, researchers said they found children who entered first grade with signs of depression and anxiety or excessive aggression were at risk of being chronically victimized by their classmates by third grade.

"Children's early mental-health problems can set the stage for abuse by their peers," said psychology Prof. Bonnie Leadbeater of the University of Victoria, who led the study.

Just as some children need extra help learning to read when they lag behind their peers, young children with mental-health problems also show signs that they can't manage the "complex social world of elementary school."

"Treating children's mental-health problems may go a long way toward reducing bullying," Leadbeater added.

In the study, teachers were asked to report on the children's symptoms of depression, anxiety and displays of physical aggression. Researchers returned at the end of the first, second and third grades to ask the children and their teachers to report on the same issues.

While 73 per cent showed few symptoms of depression and anxiety over the three years, seven per cent showed high levels throughout the course of the study. The other 20 per cent showed moderate symptoms at first that increased over time.

Children who were more prone to be aggressive when they started first grade were more likely to be victimized by their peers, perhaps in retaliation for their own acts of aggression, the researchers said.

The research was supported by grants from the Canadian Institutes of Health Research and the Social Sciences and Humanities Research Council of Canada.