Well beyond a billion students were sent home from schools as the novel coronavirus spread around the world.

In recent weeks, hundreds of millions were cleared to return, as countries began to reopen in fits and starts.

By late March, less than two months after the confirmation of the first coronavirus cases outside China, more than 90 percent of the world’s students were already affected by school closures, according to estimates by the United Nations Educational, Scientific and Cultural Organization, known as UNESCO. Stuck at home for months, they found themselves part of a global web of hastily implemented experiments in home schooling, remote learning and social distancing.

At the height of such measures in April, nearly 1.6 billion students were affected, according to UNESCO, with 194 countrywide closures. As of June 5, more than 1.1 billion students remain affected — more than 64 percent of the world’s total, with 134 countrywide closures in place.

Even in countries without school shutdowns enforced at the national level, disruptions to education remain widespread. In the United States, measures vary at the local level, but the majority of states have mandated closures through the end of the school year.

The students for whom school closures have lifted will be the subjects of a new, global experiment, as educators and policymakers try to determine what classrooms should look like during the pandemic.

Here’s how some countries around the world are handling the return.

Britain

Britain reopened its schools in early June, sending hundreds of thousands of students back to the classroom for the first time since March 18. But it was a partial reopening: Outside of England, the semiautonomous governments of Scotland, Wales and Northern Ireland have chosen to wait until August or later.

Within England, the return varied substantially, with dozens of local authorities keeping their schools shuttered. Officials pushed especially for the return of children in the equivalent of kindergarten, first grade and sixth grades — identified as “key transition years” by the British government. Going back to school is encouraged, not mandatory.

Many parents appear to have decided to keep their children at home. A survey by the National Foundation for Educational Research said 46 percent of parents were planning to do so. A union for head teachers told the BBC attendance was generally between 40 percent and 70 percent.

Brazil

In Brazil, home to the second-largest number of confirmed cases in the world, President Jair Bolsonaro has taken a laissez-faire approach to the coronavirus and publicly rejected calls to reopen schools. “What has happened in the world has shown that the people at risk are older than 60,” Bolsonaro said in a national address in late March. “So why close the schools?”

Without a coordinated national response, local officials decide on school closures. Most of the country’s schools had stopped in-person classes by late March. Despite the continued spread of the coronavirus within Brazil, some municipal governments have said they intend to reopen schools soon.

China

In mid-January, China told nearly 200 million students they would not be returning to school after their winter break — part of a broader lockdown on the virus epicenter of Hubei province and other hard-hit regions.

This early lockdown, also adopted in Hong Kong, prefigured measures that would spread around the world. But as the outbreak waned in China, parts of the country also became some of the earliest places to see children return to schools.

UNESCO said school openings in China have been “progressive,” generally starting with students in the final year of their secondary school education. In Wuhan, the pandemic’s initial epicenter, schools reopened in early May, but children had to pass through temperature checks, wear masks and enter and leave at specific times to avoid crowding.

Denmark

Denmark announced it would close schools on March 11. Just a month later, it became the first country in Europe to reopen them, with almost all primary schools operating by April 20.

Although some parents kept their children at home, many were confident in the government guidelines on sanitization and social distancing (including that desks must be about six feet apart and recesses staggered to avoid crowds). Older children went back to school in late May.

So far, there have been no signs of a coronavirus resurgence — new cases continued to decline as schools reopened, a trend also seen in some other European countries. In Norway, which began reopening April 20, Prime Minister Erna Solberg told NRK broadcaster that it might not have been necessary to close schools, but that she did not regret the decision.

Japan

Japan closed its schools later than some of its neighbors, with Prime Minister Shinzo Abe asking only in late February for schools to shut their doors. In March, the Japanese government announced it would not extend this request and would leave the decision up to municipalities, which would have guidelines to follow.

Some schools began reopening in early May, with students in their first or last year prioritized, and others asked to begin a few weeks later. Some schools in hard-hit cities or regions are to remain closed, while schools that reopen are undertaking a variety of measures to prevent overcrowding, including smaller classes, face masks and staggered start times.

Japan is concerned about the possibility of a second wave of infections. After recording no new cases from April 30 to May 22, the city of Kitakyushu in Fukuoka prefecture saw 119 cases in just 11 days — including 11 pupils from four elementary and junior high schools — prompting an order to re-close schools.

New Zealand

New Zealand entered its strictest level of lockdown with mandatory school closures on March 23, when it had confirmed 102 cases. But within six weeks, the country announced it would be easing these restrictions because of positive signs about the spread of the virus.

In late April, the government relaxed the lockdown from Level 4 to Level 3, with schools reopening but parents told to keep their children home if possible. On May 18, it was dropped to Level 2, allowing hundreds of thousands more students to return to the classroom.

Under the current standards, as the country approaches zero infections, there are few restrictions on healthy children. The government said “people need to play it safe and continue to take sensible health and safety precautions.”

Nigeria

Nigeria announced it would close all schools on March 19. At the time, it had 12 confirmed cases, though that number has bloomed to more than 11,000, with 333 confirmed deaths so far. More than two months later, schools remain closed. The government has indicated it hopes to allow local governments to reopen schools in the coming weeks, despite a surge in cases.

South Korea

In late February, the South Korean government told students their break would be extended by one week. It was then extended by two more, and then indefinitely as the coronavirus spread. Schools began to reopen months later in late May, with high school seniors returning first.

That initial reopening was delayed by a week after an outbreak in Seoul’s nightlife district of Itaewon. And just days after the first students set foot back in the classroom, hundreds of schools were closed after a sudden spike in new cases.

The students who have gone back must adhere to a variety of measures designed to limit any potential spread, including plastic screens over their desks, masks and temperature checks. But the government has been determined to reopen, noting that children had not even been kept at home during the Korean War.

“I believe that we cannot fail the dreams and future of our children because of the current difficulties,” Prime Minister Chung Sye-kyun said this week.

South Africa

South Africa announced it would close all schools indefinitely on March 18. The last years of primary and secondary school, grades 7 and 12, respectively, were supposed to return to school at the start of June; that plan was abandoned after teachers’ unions and governing associations refused to back it.

Teachers have said they do not have enough protective equipment to keep themselves and their students safe. In response to the backlash, South Africa’s Department of Basic Education said school reopening would be delayed by a week so schools could prepare for the arrival of students.

Taiwan

Taiwan, with fewer than 500 confirmed coronavirus cases, has controlled the spread of the infection without taking many of the draconian measures seen elsewhere.

This extends to school closures: Although the government extended winter break for an extra two weeks in February, it reopened schools as normal by Feb. 25 and most education has run on a regular schedule since then, albeit with strict sanitary measures in place.

Schools and universities close if they confirm a case among students and staff, but that has been rare: Only one school had shut its doors by the start of April, along with a handful of universities.