A team of researchers led by an epidemiologist at Mount Sinai School of Medicine and University of Iceland has found a correlation between the age at which children with attention-deficit/hyperactivity disorder (ADHD) begin taking medication, and how well they perform on standardized tests, particularly in math.

The study, titled, "A Population-Based Study of Stimulant Drug Treatment of ADHD and Academic Progress in Children," appears in the July, 2012, edition of Pediatrics, and can be viewed online on June 25. Using data from the Icelandic Medicines Registry and the Database of National Scholastic Examinations, the researchers studied 11,872 Icelandic children born between 1994 and 1996. The children started medication for ADHD at different times between fourth and seventh grades.

The findings showed that children who began drug treatment within 12 months of their fourth-grade test declined 0.3 percent in math by the time they took their seventh-grade test, compared with a decline of 9.4 percent in children who began taking medication 25-to-36 months after their fourth-grade test.

The data also showed that girls benefited only in mathematics, whereas boys had marginal benefits in math and language arts.

"Children who began taking medications immediately after their fourth-grade standardized tests showed the smallest declines in academic performance," said the study's lead author Helga Zoega, PhD, Post Doctoral Fellow of Epidemiology at Mount Sinai's Institute for Translational Epidemiology. "The effect was greater in girls than boys and also greater for children who did poorly on their fourth grade test."

Stimulants are widely used in the United States as a therapeutic option for children with inattention, impulsivity, and hyperactivity associated with ADHD. The medications are less frequently used in Europe, although their use in Iceland most closely resembles the U.S. Long-term follow-up studies of stimulant use and academic performance are scarce, according to the researchers.