The study, by the Schools Health Education Unit (SHEU) also revealed that 16% of kids in that age group feel nervous about hanging out with other pupils during school breaks because of the threat of being bullied.
Fact File
Other findings in the report
28% said they had been scared or upset by an adult stranger
78% said they didn't think they would smoke when they're older
71% said their parents had spoken to them about drugs
Girls were particularly concerned about their appearance, with 16% of them saying they had been picked on because of how they looked.
A SHEU spokesman said it was unacceptable that so many kids were being targeted by bullies.
"It's not about shoving and name-calling. It's often more subtle," he said.
The study also threw up some other interesting statistics.
For example, the number of boys reading in their spare time dropped from 29% to 17% between 1997 and 2002.
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