Math scores on the so-called National Assessment of Educational Progress (NAEP) test, often dubbed "the nation's report card," went down for the first time in a quarter century, meaning that randomly selected fourth- and eighth-grade students performed worse in the key subject.

But the dip in the biennial NAEP exam "doesn't come as a big surprise," U.S. Education Secretary Arne Duncan said, even though Peggy Carr, the federal official who oversees the tests, said she did not expect the poor result, according to USA Today.

"This isn't a pattern that we saw coming," Carr noted. "In that sense, it was an unexpected downturn. But we'll see. I think the bigger point is that we'll see if this is going to be a trend that will continue."

Test scores for students in fourth and eighth grades dropped two points to 240 and three points to 282, respectively, from 2013 to 2015, Reuters detailed. The exam is scored on a scale of 0 to 300.

William Mathis, the managing director of the National Education Policy Center at the University of Colorado in Boulder, said experts are still trying to determine what exactly is behind the dip, the newswire added. "At this point. we don't know if it's a one-year fluke or something else," Mathis said.

Carr, meanwhile, insisted that test fatigue on the part of students was not to blame for the poor results as researchers found no evidence that test takers in 2015 were any less engaged in the exam than their counterparts in past years, USA Today noted.

Nevertheless, the Obama administration last week pushed to limit the time students spend taking and preparing for standardized tests, concerned that testing is "consuming too much instructional time and creating undue stress for educators and students," according to the newspaper.

Mathis told Reuters that the use of rigorous standardized testing initiatives in schools over the past 14 years can, in fact, exhaust students and educators. But economic difficulties and inequalities could also account for the decline in test scores, he added.