Fast-food consumption isn’t merely connected to increases in pants size — it’s also tied to significant decreases in test scores among school children, according to a new national study.

Researchers at Ohio State University used data from a nationally representative sample of about 11,700 children to measure how fast food might be affecting classroom performance. The study measured how much fast food the children were eating at age 10 and then compared the consumption levels with test results in reading, math and science three years later.

What they found is that even small increases in the frequency with which the students ate fast food were associated with poorer academic test results. Habitual fast-food eaters — those who ate fast food daily — saw “test score gains that were up to about 20 percent lower than those who didn’t eat any fast food.”

The connection held true even after the researchers took into account more than a dozen other factors about the children’s habits and backgrounds that might have contributed to the association between fast-food consumption and poorer academic performance, including fitness, broader eating habits, socioeconomic status and characteristics of their neighborhoods and schools.

“Our results show clear and consistent associations between children’s fast food consumption in 5th grade and academic growth between 5th and 8th grade,” the researchers wrote.

More than half of the students the researchers observed ate fast food one to three times a week, and nearly three-quarters of them ate fast food at least once a week.

The study observed children’s eating habits in 2004 and therefore could point to fast-food consumption levels that are no longer representative of current trends. But there’s reason to believe little has changed. Nearly one-third of American children between the ages of 2 and 11 — and nearly half of those ages 12 to 19 — eat or drink something from a fast-food restaurant every day, according to a study from 2008. And fast food still accounts for about 13 percent of total calories eaten by children and teenagers ages 2 to 18 in the United States.

Kelly Purtell, the study’s lead author, is careful to point out that while there’s a strong suggestion that feeding children fast food negatively affects their academic performance, the study falls short of establishing a definitive causal connection. Although her team can’t prove the diet quirk caused lower test-score gains, the group insists that fast-food consumption helps explain at least part of the performance gap among the students.