New research from Iceland suggests kids who get early treatment for their attention-deficit/hyperactivity disorder don't have as much trouble on national standardized tests as those who aren't prescribed medication until age 11 or 12.

Common medications used to treat ADHD include stimulants such as Vyvanse, Ritalin and Concerta.

"Their short-term efficacy in treating the core symptoms of ADHD -- the symptoms of hyperactivity and attention and impulsivity -- that has been established," said Helga Zoega, the lead author on the new study from the Mount Sinai School of Medicine in New York.

"With regard to more functional outcomes, for example academic performance or progress, there's not as much evidence there as to whether these drugs really help the kids academically in the long term," she told Reuters Health.

To try to answer that question, Zoega and colleagues from the United States and Iceland consulted prescription drug records and test scores from Icelandic elementary and middle school students between 2003 and 2008.

Out of more than 13,000 kids registered in the national school system, just over 1,000 were treated with ADHD drugs at some point between fourth and seventh grade - 317 of whom began their treatment during that span.

Kids with no record of an ADHD diagnosis tended to score similarly on the standardized math and language arts tests given in fourth and seventh grade. Those who were medicated for the condition were more likely to have their scores decline over the years - especially when stimulants weren't started until later on.

For math exams in particular, students who started on stimulants within one year of their fourth grade tests had an average score decline of less than one percent between that and their seventh-grade exam - compared to a more than nine percent drop for those who didn't get treated until sixth or seventh grade.

The difference was especially clear for girls, Zoega and her colleagues reported Monday in Pediatrics.

According to the Centers for Disease Control and Prevention, parent reports suggest close to one in 10 kids and teens in the U.S. have ever been diagnosed with ADHD, and two-thirds of those with a current diagnosis are treated with medication such as stimulants.

J. Russell Ramsay, who studies ADHD at the University of Pennsylvania's Perelman School of Medicine in Philadelphia, said kids' trouble in school is usually one of the top reasons parents seek help for their ADHD.

When it comes to school performance, "There are obvious benefits of getting started sooner rather than later," he told Reuters Health.

"Especially if students are struggling later on, this study would suggest it may be at the very least useful to explore and consider certain treatment options."

Families can see a mental health professional and discuss the pros and cons of medication and other treatments, he added.

The researchers noted they didn't have information on kids' exact underlying ADHD diagnosis or its severity, and they also couldn't tell whether youngsters were getting behavioral treatment or extra school help along with stimulants.

"Not all kids need medication," Zoega said. "It's important to think about whether alternative treatment options, whether earlier intervention with those could have a beneficial effect."

ADHD drugs can come with side effects, including appetite loss, sleep problems and stomach aches.

One of the other researchers on the study has received funding from pharmaceutical companies, including those that make stimulant drugs for ADHD.

"Medications are probably still the reflex response, with a good evidence base," said Ramsay, who wasn't involved in the new research. "But there are other things that can be added in later or concurrently that can also provide support to the child, to the family and to the educators."