National test scores released on Wednesday showed a marked drop in students’ knowledge of U.S. history and a modest decline in civics, a sign of the pandemic’s alarming reach, damaging student performance in nearly every academic area.

The pandemic plunge in U.S. history accelerated a downward trend that began nearly a decade ago, hitting this recent low at a time when the subject itself has become increasingly politically divisive.

A growing number of students are falling below even the basic standards set out on the National Assessment of Educational Progress, a rigorous national exam administered by the Department of Education. About 40 percent of eighth graders scored “below basic” in U.S. history last year, compared with 34 percent in 2018 and 29 percent in 2014.

Just 13 percent of eighth graders were considered proficient — demonstrating competency over challenging subject matter — down from 18 percent nearly a decade ago.

Questions ranged from the simple — knowing that factory conditions in the 1800s were dangerous, with long days and low pay — to the complex. For example, only 6 percent of students could explain in their own words how two ideas from the Constitution were reflected in the Rev. Dr. Martin Luther King Jr.’s “I Have a Dream” speech.

The dip in civics performance was smaller but notable: It was the first decline since the test began being administered in the late 1990s. About 22 percent of students were proficient, down from 24 percent in 2018.

President Biden’s education secretary, Miguel A. Cardona, seized on the results, admonishing politicians for trying to limit instruction in history, often on topics of race, a trend that has played out in dozens of states, typically Republican controlled.

“Now is not the time,” he said, adding that “banning history books and censoring educators from teaching these important subjects does our students a disservice and will move America in the wrong direction.”

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Since the implementation of No Child Left Behind in the early 2000s and its update during the Obama administration, federal policy has required states to test students in reading and math. Periodic testing is also required for science.

No such mandate exists for social studies. (Many state policies around testing and accountability also do not include social studies.)

While some experts have criticized standardized tests as limited in effectiveness and detrimental to students, most generally agree: What is tested drives what is taught.