One in three students with attention-deficit hyperactivity disorder (ADHD) do not receive any support services at their schools, according to a national study of U.S. schoolchildren.

The study — described as the largest of its kind — found that at least one in five students with ADHD receive no school-based services even when they experience significant academic and social impairment. The services gap appeared to be especially pronounced for adolescents from non-English-speaking or low-income families.

Researchers from the Centers for Disease Control and Prevention, Lehigh University, and the University of Maryland took part in the study. The findings, published in the Journal of Attention Disorders, are based on data for 2,495 youths with ADHD aged 4 to 17 from the National Survey of the Diagnosis and Treatment of ADHD and Tourette Syndrome.

Students from every state were represented, according to one of the chief researchers.

“I would hope people who work in schools, or parents — really anyone concerned about these kids — would realize there’s a gap between those students who need school support for ADHD and those who actually get it, particularly for students on the middle- and high-school level,” said lead study author George DuPaul, a professor of school psychology and associate dean for research in the College of Education at Lehigh.

ADHD is one of the most common childhood neurodevelopmental disorders, characterized by inattention, concentration difficulties, and problems with impulse control. Federal estimates say 11 percent of children will receive a diagnosis, but many students with the disorder are missed, especially girls, whose symptoms may defy ADHD’s largely male stereotypes. The disorder often continues into adulthood, with about 5 percent of adults diagnosed. It may be treated with medication or behavioral therapy.

The study findings are based on parent-reported data about the kinds of services their children have received at school.

The research article states, “We found a critical gap in the percentage of students with ADHD who need school support due to academic or social impairment and the percentage of students who currently receive services.”

Included in the one in five students with those impairments who did not get school-based services were children and youths with ADHD who had repeated a grade or been expelled from a school.

The study also found that less than 43 percent of the students with ADHD had individualized education plans (IEPs) for special education services and that less than 14 percent had so-called Section 504 plans, which, by federal law, allow some students with physical or mental challenges special accommodations such as additional time to take tests or complete assignments.

Children from non-English-speaking families were less likely than others to receive services, including accommodations and protections under 504 plans, the authors found. Secondary students with ADHD were also less likely to get school support than elementary school children, even if their levels of impairment were the same or greater than the younger children.

“Children with ADHD may benefit from initiatives to proactively identify students with this disorder and directly target their specific impairments with evidence-based intervention approaches,” the authors wrote.

They also recommended initiatives like more bilingual mental health workers “to increase awareness of and access to effective school supports and interventions.”