Self-injury, such as cutting, begins as early as the third grade (7-year-olds), says a new study.
Researchers at the University of Denver, in one of the first studies of self-injury rates among young people, found that even the very young hurt themselves by cutting, burning, carving, piercing and hitting themselves.
"A lot of people tend to think that school-aged children, they're happy, they don't have a lot to worry about," said study co-author Benjamin Hankin of the University of Denver, reported Reuters.
"Clearly a lot more kids are doing this than people have known."
The study was conducted using interviews with 665 children between seven and 16 in the Denver area and in New Jersey.
It found that about eight percent of third-graders intententionally hurt themselves.
Most had done it more than once.
As children got older, the rate of intentional injury increased.
The study found that 13 percent of ninth graders had cut, burned or hit themselves.
"It's unfortunately probably more common than we want to think," said Hankin, reported the Associated Press.
WebMd reported that before high school, self-injury is equally common in boys and girls but by high school girls were three times more likely to hurt themselves.
Researchers also found that girls were more likely to cut or carve their skin and boys more likely to hit themselves.