Nearly two years into the pandemic, America's students are still suffering. Disruptions to in-person schooling have caused significant learning loss in math and reading, and widened racial achievement gaps. Millions of students have a basic need: more time in the classroom.

The good news is that public school districts have resources to make that happen, thanks to the Covid relief bills passed by Congress. Yet with coronavirus cases rising and a new variant adding to the uncertainty, some schools are once again curtailing in-person instruction. Even if limited in duration, such closures are wrong — and risk doing irreparable academic harm to the students who can least afford it.

At this point, the evidence against remote learning is overwhelming. A November study from the National Bureau of Economic Research compared standardized test scores from schools in districts that fully reopened early in the pandemic with those that remained at least partly virtual. While passing rates in math slumped by an average of 14.2% overall, the decline was smaller for districts that returned to in-person instruction. Drops in reading scores were heavily concentrated in areas with large populations of minorities and low-income students, which were slower to reopen.

Though students have largely returned to the classroom, the vast majority still have ground to make up. Additional instruction — in the form of longer school days, summer classes and individual tutoring — is critical for those at greatest disadvantage. Instead, some districts, from Bellevue, Washington, to Brevard County, Florida, have done the opposite. Citing staffing shortages related to teacher exhaustion, among other excuses, schools have been adding last-minute vacation days, often with little notice for parents. Leading the mental-health relief trend, officials in Detroit announced that schools would conduct in-person instruction only four days a week during December, with Fridays all remote.

Policymakers should require districts to demonstrate that they're using these funds to keep schools open. Meanwhile, federal and state officials should better prepare schools to stay open during a possible winter surge driven by the Omicron variant. On-site vaccination clinics and access to rapid tests should be expanded. School leaders should adopt "test-to-stay" strategies, which allow more students to continue in-person learning, even if classmates test positive for the virus.