In 1918 and 1919, the Spanish flu infected an estimated half a billion people—nearly a third of the population of the planet at the time—and killed between 17 and 50 million, including between 500,000 and 850,000 Americans (the wide variances in numbers are due to lack of testing capability and the limits of the healthcare system of the time).
Most schools in the United States closed in fall of 1918, as the deadly second wave of the 1918 flu epidemic became apparent. A person from 2020 going back to October of 1918 would find the scene familiar: mask mandates, stay-at-home orders, social distancing, and closed businesses, schools, and churches. Studies after the fact showed that cities which enacted more than one of these protective measures prevented up to 50 percent of possible infections.
A few cities—New York, Chicago, and New Haven, Connecticut—tried something slightly different. They kept schools open on the theory that the school was the most hygienic environment available to most of their students.
In New York and Chicago, this was almost certainly true. More than 70 percent of New York City’s nearly 1 million schoolchildren lived in crowded tenements, often with shared kitchens or bathrooms, making clean social distancing at home all but impossible. The year 1918 was the peak of the Progressive Era, which promoted hygiene and healthcare in schools, meaning there were nurses on hand as well, to monitor the health of the student body.
While the 1918 flu epidemic hit New York City harder than it did most parts of the United States, as was the case with with COVID-19, it was able to begin mitigating the damage earlier than other major cities. Chicago also did better than one might expect. However, studies that came out in 1919 and 1920 praising the decisions to keep schools open have been debunked; families of the children in these schools suffered particularly hard, with a nearly 50 percent infection rate and double the deaths of families whose children did not go to school.