President Donald Trump is pushing U.S. schools to open classroom doors wide. In some districts that have followed his instructions, they’re slamming shut again.

Schools that reopened fully and early are seeing hundreds of students, staff and teachers put into quarantine as COVID-19 spreads. Some are closing buildings opened just days ago. Others are frantically looking for workarounds — and for the money to pay for them. In Memphis, Tenn. and Irvine, Calif., teachers must sign liability waivers in case they get sick.

Nationally, most districts are ignoring Trump’s full-speed-ahead advice. New Jersey on Wednesday reversed course on mandatory in-person classes, and Boston won’t attempt them.

Still, too many insist on putting educators and communities at risk, said Lily Eskelsen Garcia, president of the National Education Association and a sixth-grade teacher in Salt Lake City.

“There is no one, maybe besides parents, who wants kids back in school as much as teachers do,” Eskelsen Garcia said. “We hate online learning, too. We’re throwing our computers against the wall, too. But we want to do it when and where we can do it without killing anybody.”

Trump has been demanding schools reopen so that parents are able to work — part of a bid to restart the economy and create the impression the U.S. is returning to normal ahead of the November election. Yet the virus is continuing to rage across parts of the U.S., with the country’s death toll at about 165,000.

The president has tried to force reopenings by saying that half the money for schools in the next round of stimulus legislation should be reserved for those that open their doors. On Wednesday, at an event with parents and educators, he criticized districts trying to use halfway measures to bring students back to class, like combining virtual learning with class time and having fewer kids in the school at a time.

At a later briefing, the White House released simple advice for reopening: Students and staff should assess their own health, understand the symptoms of COVID-19, wash their hands, socially distance around vulnerable people, and maintain good ventilation. The guidelines also said schools should “encourage” wearing masks.

Trump said there’s no substitute for traditional schooling.

“When you have students sitting at home playing with a computer, it’s not the same,” he said at the briefing. “When you sit at home in a basement looking at a computer, your brain starts to wither away.”

Nationally, just over half of students in kindergarten through high school will attend school virtually in the fall, while 44 percent will take classes in person in some form, according to a survey of public school districts by Burbio, a New York-based data service. And many of those going back to in-person classes won’t be going back full time, with schools staggering attendance to groups small enough to maintain social distancing. Some 66 percent of students across the 200 largest districts are taking virtual-only classes, Burbio found.

Large urban districts that are starting the year online include Atlanta, Houston, Boston, Los Angeles and Chicago. Some have written off the entire semester for in-person classes.

Boston Mayor Marty Walsh announced Wednesday that public-school students will not be showing up in person in the fall. In New Jersey, Gov. Phil Murphy abandoned a requirement that New Jersey’s 2,500 public schools conduct in-person teaching, allowing some to use distance-only learning when the academic year begins in early September.

Others are setting dates for students to come back to class that may roll forward, depending on the pandemic’s spread. In metro Atlanta, Fulton County schools — in March the first in Georgia to shut down — will bring in the youngest children and special-education students for limited hours in September and then phase in the rest. But that’s only if the infection rates in the county are low enough and dropping, said Superintendent Mike Looney.

He said he’s taken heat from parents and teachers alike, but will follow health guidelines about what’s safe. When students do return, they will be required to wear masks, he said. The district is also working to reconfigure its physical plant to allow proper distancing.

Other metro Atlanta districts have pushed forward with reopening and paid an immediate price in an area with high community spread.

In Cherokee County, north of the city, more than 900 people — most of them students, but also teachers and staff — are in quarantine just nine days after the school opened its doors because students reported infections. The high school had to close again.

The district required masks of teachers and staff but not of students, spokeswoman Barbara Jacoby said.