In an 18-year study on attention-deficit hyperactivity disorder, Mayo Clinic researchers found that treatment with prescription stimulants is associated with improved long-term academic success of children with the condition.

A related Mayo Clinic study finds that compared to children without ADHD, children with the disorder are at risk for poor long-term school outcomes such as low achievement in reading, absenteeism, repeating a grade and dropping out of school.

Both studies appear in the current edition of the Journal of Development & Behavioral Pediatrics.

Dr. William Barbaresi, a Mayo Clinic pediatrician and lead author of the reports, said the studies provide the first solid evidence of the long-term negative academic performance associated with untreated ADHD, and conclude that the best course of treatment for the disorder are medications, such as Ritalin.

“The finding that treatment with stimulant medications is associated with long-term improvement in school outcomes is significant,” Barbaresi said in a news release. “Previously, there was evidence that treatment with stimulant medications improved short-term academic performance, but there was no good evidence that long-term outcomes are better with stimulant treatment.”

Nearly two million children, about 3 to 5 percent of the total U.S. youth population, have the disorder, which affects a child’s ability to focus, concentrate and control impulsive behavior, researchers offered as background.

This disorder is so common that most school classrooms have at least one child with clinically-diagnosed ADHD, they said.

The Studies

Mayo Clinic researchers followed more than 5,000 children from the time they were born for an average 18 years. Of the children evaluated, 370 (277 boys and 93 girls) were identified as having ADHD.

Researchers matched them by age and gender to 740 children who did not meet the research criteria for having ADHD.

In addition to medical stimulants such as methylphenidate, sold as Ritalin, the study examined the effects on school outcomes of maternal age, socioeconomic background and special education services the students received.

The children treated with stimulants typically began taking medication in elementary school and received it for nearly three years or about 30.4 months. The studies found:

— Girls and boys with untreated ADHD were equally vulnerable to poor school outcomes — and girls may be at risk for being under-identified as having ADHD.

— By age 13, on average, stimulant dose was modestly correlated with improved reading achievement scores.

— Both treatment with stimulants and longer duration of medication were associated with decreased absenteeism.

— Children with ADHD who were treated with stimulants were 1.8 times less likely to be retained a grade than children with ADHD who were not treated.