These declines cut across almost all ethnic communities and income levels and are significantly more pronounced for the lowest-performing students. While the highest performing students (at the 90th percentile) saw a modest decline – 3 points in math – students at the bottom 10th percentile lost 12 points in math, a fourfold increase.

“I was surprised by the scope and magnitude of the decline,” said Peggy G. Carr, commissioner of the National Center for Education Statistics, the federal agency that administered the test earlier this year. A national sample of 14,800 9-year-olds was tested and the results were compared to tests taken by the same age group in early 2020, just before the pandemic hit the United States.

High- and low-performing students were already showing gaps before the pandemic, but now “the weakest students are falling faster,” Dr. Carr said.

In science subjects, black students lost 13 points compared to five for white students, widening the gap between the two groups. The research documented the profound effect of school closures on low-income and black and Spanish-speaking students, partly because their schools were more likely to pursue distance learning for extended periods.

The weakening of test scores means that while many 9-year-olds can show partial understanding of what they read, fewer can infer a character’s feelings from what they have read. In mathematics, pupils may know simple arithmetic, but fewer can add fractions with a common denominator.

These falls could have severe consequences for a generation of children who need to go beyond the basics in primary school to thrive later.

“Students’ test scores, even from first, second, and third grade onward, are highly predictive of their later success in school and their educational trajectories in general,” said Susanna Loeb, director of Brown University’s Annenberg Institute, which focuses on educational inequality.

The National Assessment of Educational Progress (NAEP) is the gold educational testing standard. Unlike state tests, it is standardised across the country, has remained consistent over time and does not seek to hold individual schools accountable for results, which experts say makes it more reliable.

The test results provided a snapshot of just one age group: 9-year-olds, typically in third or fourth grade. (More results for fourth and eighth graders, will be released later this fall by each state).

“This is a test that can speak bluntly to federal and state leaders about how much work needs to be done,” said Andrew Ho, a Harvard education professor and educational testing expert. He once served on the board that oversees the exam.

Over time, reading scores, and especially math scores, have generally trended upward or remained stable since the test was first used in the early 1970s. There was a period of solid growth from the late 1990s to the mid-2000s.

But over the last ten years, student results have stabilized rather than improved, while the gaps between the lowest and highest performing students have widened.

Then came the pandemic, which closed schools across the country almost overnight. Teachers taught their classes via Zoom, and students stayed home, struggling to learn online.

In some parts of the country, the worst disruption was short-lived, with schools reopening in the autumn. But in other areas, particularly in large cities with large populations of low-income students and students of color, schools remained closed for many months, and some did not fully reopen until last year.

Ho said the national tests tell the story of a “decade of progress,” followed by a “decade of inequality” and then the “shock” of the pandemic, which came as a double whammy.

“It erased progress and exacerbated inequality. Now we have our work cut out for us.

He estimates that the loss of one point in the national exam is equivalent to about three weeks of learning. This means that a high-achieving pupil who lost three points in math could catch up in just nine weeks, while a low-achieving pupil who lost 12 points would need 36 weeks, or almost nine months, to catch up – and would still be behind their more advanced peers.

There are signs that students have returned to school and are learning at an average pace, but experts say it will take more than regular school days to close the gaps created by the pandemic.

Janice K. Jackson, who ran Chicago Public Schools until last year and is now a board member of Chiefs for Change, representing state education and school district officials, said the results should be a “rallying cry” to get students back on track.

She called on the federal government to come up with big ideas, invoking the Marshall Plan, the US initiative to help rebuild Europe after World War II.

“It’s that dramatic for me,” she said, adding that politicians, school leaders, teachers’ unions and parents should put aside the many disagreements that have erupted during the pandemic. And come together to help students recover.