More kids are being diagnosed with attention deficit hyperactivity disorder (ADHD), the most common childhood disorder, according to a new study published in JAMA Pediatrics and reported by

ADHD is defined as “a persistent pattern of inattention and/or hyperactivity-impulsivity.” Youths with ADHD are more likely to have problems in school and with social relationships because they can’t sit still or are inattentive and disruptive.

For the study, researchers evaluated the medical records of nearly 850,000 children between ages 5 and 11. Scientists reviewed diagnosis rates, tests used for identifying ADHD, and the different types and manifestations of the disorder. The findings showed a 70 percent increase in ADHD diagnoses among black youth and a 90 percent increase among African-American girls.

Although the findings didn’t say why there’s been an uptick in ADHD diagnoses, some experts believe that more black parents are getting their children evaluated for the disorder. “African-American parents are obtaining more knowledge of the symptoms of ADHD and are encountering practitioners that are being more careful in discussing the symptoms and the treatments with them,” said Richard Gallagher, PhD, an associate professor of child and adolescent psychiatry at New York University’s Child Study Center.

In addition, Gallagher said that the increase in ADHD diagnoses might reflect improvements in tools that test for the disorder. But other experts warned of another possible cause: Children with histories of trauma, violence and abuse were misdiagnosed as having ADHD. (Often, post-traumatic stress disorder symptoms can be mistaken for signs of ADHD.)

Attention deficit hyperactive disorder affects about 4.6 million school-age American kids. Click here to read more.