JERUSALEM -- As the United States and other countries anxiously consider how to reopen schools, Israel, one of the first countries to do so, illustrates the dangers of moving too precipitously.
Confident it had beaten the coronavirus and desperate to reboot a devastated economy, the Israeli government invited the entire student body back in late May.
Within days, infections were reported at a Jerusalem high school, which quickly mushroomed into the largest outbreak in a single school in Israel, possibly the world.
The virus rippled out to the students' homes and then to other schools and neighborhoods, ultimately infecting hundreds of students, teachers and relatives.
Other outbreaks forced hundreds of schools to close. Across the country, tens of thousands of students and teachers were quarantined.
Israel's advice for other countries?
"They definitely should not do what we have done," said Eli Waxman, a professor at the Weizmann Institute of Science and chairman of the team advising Israel's National Security Council on the pandemic. "It was a major failure."
The lesson, experts say, is that even communities that have gotten the spread of the virus under control need to take strict precautions when reopening schools. Smaller classes, mask wearing, keeping desks 6 feet apart and providing adequate ventilation, they say, are likely to be crucial until a vaccine is available.
"If there is a low number of cases, there is an illusion that the disease is over," said Dr. Hagai Levine, a professor of epidemiology and chairman of the Israeli Association of Public Health Physicians. "But it's a complete illusion."
"The mistake in Israel," he said, "is that you can open the education system, but you have to do it gradually, with certain limits, and you have to do it in a very careful way."
Israel's handling of the pandemic was considered successful at first. The country of 9 million quickly closed its borders, shuttered schools in mid-March and introduced remote learning for its 2 million students. In April, Passover and Ramadan were celebrated under lockdown.
By early May, infection rates had fallen from over 750 confirmed cases a day to double digits. The youngest students, grades 3 and under, and older students taking final exams returned in small groups, splitting the week to take turns using classrooms.
Emboldened by the dropping infection rates, the government completely reopened schools on May 17, the day a new government was sworn in.
In his inaugural speech, Prime Minister Benjamin Netanyahu promised a new budget that would deliver three things: "Jobs, jobs, jobs." His new education minister, Yoav Gallant, said that the school system's "immediate mission" was to allow parents to return to work with peace of mind.
Inna Zaltsman, an Education Ministry official, said administrators also wanted "to return the children to routine as much as possible, for their emotional and pedagogic well-being."
Shopping malls, outdoor markets and gyms had already reopened, and soon houses of worship, restaurants, bars, hotels and wedding halls did too. Netanyahu told Israelis to grab a beer and, while taking precautions, "Go out and have a good time."
In hindsight, that advice was wildly premature.
That same day, a mother phoned a teacher at Jerusalem's Gymnasia Ha'ivrit high school. Her son, a seventh-grade student there, had tested positive for the virus.
By the next day, the school confirmed another case in the ninth grade. Ultimately, Israeli officials said, 154 students and 26 staff members were found to be infected.
"There was a general euphoria among the public, a sense that we had dealt with the first wave well and that it was behind us," said Danniel Leibovitch, Gymnasia's principal. "Of course, that wasn't true."
The Education Ministry had issued safety instructions: Masks were to be worn by students in fourth grade and higher, windows kept open, hands washed frequently and students kept 6 feet apart whenever possible.
But in many Israeli schools, where up to 38 children squeeze into classrooms of about 500 square feet, physical distancing proved impossible.
Unable to comply with the rules, some local authorities ignored them or simply decided not to reopen at full capacity.
Then a heat wave hit. Parents complained that it was inhumane to make children wear masks in steaming classrooms where open windows nullified the air conditioning.
In response, the government exempted everyone from wearing masks for four days, and schools shut the windows.
That decision proved disastrous, experts say.
"Instead of canceling school in those days, they just told the kids 'OK, well you have to stay in the class with the air conditioning on and take your masks off,' so you have no ventilation really," said Dr. Ronit Calderon-Margalit, a professor of epidemiology at Hebrew University-Hadassah Braun School of Public Health. "You have the ideal circumstances for an outbreak."
The Gymnasia became a petri dish for covid-19.
When the first case was discovered, the student's classmates, teachers and other contacts were quarantined. After the second case, which was not directly linked to the first, the school was closed and everyone was instructed to quarantine for two weeks. All students and staff were tested, often waiting in line for hours.
About 60% of infected students were asymptomatic. Teachers suffered the most and a few were hospitalized, the principal said.
Seeking to contain the contagion, the Education Ministry vowed to shut any school with even one covid-19 case. It ultimately closed more than 240 schools and quarantined more than 22,520 teachers and students.
When the school year ended in late June, the ministry said, 977 pupils and teachers had contracted covid-19.
But the Health Ministry, lacking the infrastructure and resources, did not make contact tracing a priority. In the Gymnasia case, Waxman said, nobody even identified which buses the students had ridden to school on.
Outside school walls, the coronavirus returned with a vengeance. Covid-19 wards that had closed with festive ceremonies in late April began filling again, with confirmed infections spiraling to about 800 a day by late June and over 2,000 a day by late July.
Some blamed the hasty school reopening as a major factor in the second wave. Siegal Sadetzki, who resigned in frustration last month as Israel's director of public health services, wrote that insufficient safety precautions in schools, as well as large gatherings such as weddings, fueled a "significant portion" of second-wave infections.
But others said singling out schools was unfair when the real problem was that everything reopened too quickly.
"The single super-spreader event in the Gymnasia just happened to be in a school," said Dr. Ran Balicer, an Israeli health care official and adviser to the prime minister on the pandemic. "It could have happened in any other setting."