Recent papers have also cast doubt on whether medication’s benefits last as long as those from therapy.

“There was lost opportunity to give kids the advantage of both and develop more resources in schools to support the child — that value was dismissed,” said Dr. Gene Arnold, a child psychiatrist and professor at Ohio State University and one of the principal researchers on the study, known as the Multimodal Treatment Study of Children With A.D.H.D.

Another co-author, Dr. Lily Hechtman of McGill University in Montreal, added: “I hope it didn’t do irreparable damage. The people who pay the price in the end is the kids. That’s the biggest tragedy in all of this.”

A.D.H.D. narrowly trails asthma as the most frequent long-term medical diagnosis in children. More than 1 in 7 children in the United States receive a diagnosis of the disorder by the time they turn 18, according to the Centers for Disease Control and Prevention. At least 70 percent of those are prescribed stimulant medication like Adderall or Concerta because, despite potential side effects like insomnia and appetite suppression, it can quickly mollify symptoms and can cost an insured family less than $200 a year.

Comprehensive behavioral (also called psychosocial) therapy is used far less often to treat children with the disorder largely because it is more time-consuming and expensive. Cost-conscious schools have few aides to help teachers assist the expanding population of children with the diagnosis, which in some communities reaches 20 percent of students. Many insurance plans inadequately cover private or group therapy for families, which can cost $1,000 a year or more.