Those problems are tied to a lower quality of life and an increased risk of needing extra help in school, according to findings reported in the Archives of Pediatrics & Adolescent Medicine.

"Our study pretty convincingly shows that the vast majority of kids do very well after a mild traumatic brain injury," or concussion, said Keith O. Yeates of Nationwide Children's Hospital in Columbus, Ohio. "The not-so-good news is that there is a small group of kids who have symptoms up to a year after their injury."

Concussion is by far the most common form of brain injury and has received increasing attention in the media. Yeates said millions of American kids get a concussion every year, but many don't go to the hospital.

In the new study, he and his colleagues followed 186 kids aged eight to 15 who came to the emergency department with a concussion. They compared those with a group of children with other kinds of injuries to try to account for the fact that kids who hurt themselves may be different than their peers.

Children with brain injuries were more likely to have both "somatic" symptoms like headache, fatigue and balance problems, and cognitive symptoms like forgetfulness and attention problems.

The somatic symptoms tended to wane over time, but in some cases the cognitive problems persisted -- particularly for those kids who lost their consciousness when they hit their head or had abnormal results on an MRI scan.

Yeates estimates that about 10 percent to 15 percent of the children with loss of consciousness continue to have cognitive problems for months after their injury.

"Right after injuries we know that if we tell parents what they can expect, that actually helps reduce symptoms because you don't have parents who are anxious, and kids who are anxious," he said.

The study is based on parents' assessments of their child's symptoms and can't prove that the symptoms were necessarily caused by the brain injury. But Yeates said he felt certain that is the case, because the symptoms were more common with severe injuries.

He said children should see a doctor if they notice ongoing problems such as headache or fogginess after a concussion.

SOURCE: bit.ly/zuq8bp Archives of Pediatrics & Adolescent Medicine, online March 5, 2012.

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