Students taking attention-deficit hyperactivity disorder (ADHD) medication don’t perform better in school than their peers who do not use the drugs, a new study concludes.

Boys taking the drugs performed worse than those with a similar number of symptoms who didn’t use ADHD medications, The Wall Street Journal reports. Girls taking the medication reported having more emotional problems.

The study included almost 4,000 Canadian students, who were followed over an average of 11 years. It was published by the National Bureau of Economic Research, a nonprofit economics research firm.

Experts say they are surprised the drugs do not seem to translate into better grades, since they appear to enhance memory. A study published in April in Pharmacology Biochemistry and Behavior found ADHD drugs seem to improve memory in children with the disorder.

A study known as MTA examined the long-term effects of ADHD treatment in 579 children, and did not find improvements in educational outcomes six to eight years later. The newspaper notes the findings of these studies suggest medication by itself is not enough to boost academic achievement.

A study released in April by the Partnership for Drug-Free Kids and MetLife Foundation found in 2012, one in eight teens (about 2.7 million) reported having misused or abused Ritalin or Adderall at least once in their lifetime, and 9 percent of teens (about 1.9 million) reported having misused these drugs in the past year.