Even before the pandemic upended school, test scores in both reading and math declined for 13-year-old students, the first drop registered in a half century in testing meant to measure student proficiency over time.

The data showed declines among the lowest-performing students, but not those at the top, suggesting that educational gaps that pervade the U.S. system are becoming larger, not smaller.

Peggy Carr, commissioner of the National Center for Education Statistics, has been working with these data for 28 years and couldn’t believe the results when she saw them. She was shocked to see an absolute decline. “I had to ask the question again of my staff. `Are you sure?' I asked them to go back and check,” she said.

The National Assessment of Educational Progress for decades has been measuring student performance in a variety of academic subjects to chart progress — or lack thereof, and dubbing the data the “Nation’s Report Card.” The results released Thursday, based on a nationally representative sample of children, compared scores of 9- and 13-year-olds to those in the early 1970s and in 2012.

Student scores remained, across the board, higher than they were a half century ago. But the new results showed overall declines for 13-year-olds since 2012, with drops concentrated among the lowest-performing students. Similar drops have also been registered on a separate, similar assessment designed to measure short-term trends, with those scores declining for those at the academic bottom and rising for those at the top.

“This is more discouraging news about our students who are struggling to learn,” Carr said. “Our struggling students are struggling more than they ever have before.”

The new report finds scores have fallen for Black and Hispanic students since 2012 and remain flat for White children, widening the racial achievement gap. This year also revealed a gender gap, as nine-year-old boys’ math scores stayed steady while girls’ scores fell compared to 2012.

The results add to the evidence that American schools are not just failing many students, but that the problem is actually getting worse.

“We are disappointed to see that scores have stagnated or dropped since 2012, and we are particularly concerned to see that results among the lowest-performing students have dropped,” said Carissa Moffat Miller, CEO of the Council of Chief State School Officers.

Education Secretary Miguel Cardona has said he hopes that U.S. schools will not just return to their old ways post-pandemic but that they will create stronger systems to help all learners. These data make clear how hard that may be, given the academic slide over the past decade.

The tests were administered in the 2019-20 school year, before the pandemic closed schools. Many experts expect further declines stemming from the substandard, online education that followed. National tests will be administered this school year among 9-year-olds, ahead of the normal schedule, to see if those fears came to pass.

Testing had been scheduled for 17-year-olds in spring 2020, but it was cancelled due to school closures. The tests had already been administered for 9- and 13-year-olds, offering the opportunity to compare performance immediately before and after school closings.

When compared to 2012 results, performance fell for 13-year-olds in both reading and math. On a 500-point scale, 13-year-olds scored an average of 280 in math in 2020, down from 285 in 2012. On the reading portion, the scores dropped from 263 to 260. Both shifts were statistically significant.

Among 9-year-olds, there was no statistically significant difference from 2012 in math or reading, up or down.

The national tests are better at explaining what happened than why, though there were some clues. A survey that accompanied the test results found increases in the number of students who said they never or hardly ever read for fun on their own time. In 1984, 9 percent of 9-year-olds said reading for fun was rare. That rose to 11 percent in 2012 and to 16 percent in 2020.

Among 13-year-olds, in 1984, 8 percent said they never or hardly ever read for fun, rising to 22 percent in 2012 and 29 percent in 2020.

“Something different is happening from the side of the students and what they are actually doing to build their skill level in reading,” Carr said. Students who say they don’t read for fun score lower on the tests, she said. But she said the cause and effect are not clear: Are children not reading and therefore scoring lower on tests? Or are their reading skills deficient so they don’t want to read?

The report also found a drop in the share of 13-year-olds, who are typically in the seventh or eighth grade, who are taking algebra or pre-algebra. Some middle schools are working to teach algebra to more kids at a younger age, aiming to address achievement gaps that can be exacerbated by ability grouping. But overall, it appears that fewer middle-schoolers are on that fast-paced math track.

The picture of academic achievement looks rosier when recent scores are compared to those when the testing began — for reading in 1971 and for math in 1973. Average scores have improved for reading and math in both age groups. Over that half-century horizon, Black and Hispanic students recorded the biggest gains.