The number of U.S. children diagnosed with attention-deficit hyperactivity disorder (ADHD) is on the rise, with the largest increase seen in girls and Hispanic children, according to a new study.

The rate of ADHD among children ages 5 to 17 increased 43 percent from 2003 to 2011, HealthDay reports. In 2011, an estimated 12 percent of American children had ever been diagnosed with ADHD, researchers from George Washington University found.

The study found ADHD is still almost twice as common among white children compared with Hispanic children (14 percent versus less than 8 percent). Between 2003 and 2011, ADHD diagnoses increased 83 percent among Hispanic children, compared with 46 percent among white children.

While twice as many boys were diagnosed with ADHD compared with girls, the prevalence among girls rose 55 percent during the study period, from 4.3 percent in 2003 to 7.5 percent in 2011.

The findings are published in the Journal of Clinical Psychiatry.

Lead researcher Sean Cleary said it is not clear whether the incidence of ADHD is increasing among girls and Hispanic children, or whether the findings are the result of a tendency to over-diagnose the condition.

Cleary said it is possible that the increase among Hispanic children is a sign of a growing acceptance of ADHD in the community, or the wider availability of mental health resources in Spanish. He added the increase in diagnoses in girls may reflect a growing awareness that girls with ADHD are more likely to have problems with daydreaming, while boys’ symptoms often get them labeled as troublemakers.

The researchers noted it is important to determine why ADHD diagnoses seem to be increasing, because children with the condition often are prescribed stimulant drugs like Ritalin. While these drugs can help children focus and stay on task, critics are concerned the drugs may be over-prescribed, the researchers note in a university news release.