With New York City and other districts across the United States starting to bring children back to school in person, at a moment of heightened medical complexity, school nurses are being asked to do their regular jobs, but also to take on new responsibilities.

Kenya Brown, the school nurse for a public school in Jamaica, Queens, for grades six through 12, said that before the school reopened on Oct. 1, she had planning meetings with the building management team, the custodians, and the people in charge of food and school safety. They were figuring out new protocols for how students would enter the building, for security checking temperatures, for isolation rooms where children who developed symptoms during the school day could go for evaluation.

With many families opting to continue with remote learning, her school had relatively few students returning last week. They all were scanned for fever on entering the school. One student who was alone in a classroom had her head down on the desk and was sent to the nurse for another temperature check. But Ms. Brown said, actually she was not sick, just “a little bored, wondering, what am I doing here?”

School nurses have also been staying in touch with families by phone, Ms. Brown said, “in order for us to make sure the students are well taken care of, even at home, we have to keep calling, touching base with parents, with students.” They’ve already called many families: “Some students have lost parents and grandparents,” she said. “It’s a humbling situation.”

[On Sunday, Mayor Bill de Blasio announced new restrictions, including closing about 300 public and private schools in Brooklyn and Queens neighborhoods that have been experiencing rising positivity rates.]

Early school nurses battled the infections of urban poverty and helped defeat forgotten epidemics, and now, as many communities attempt to restart their schools during a pandemic, school nurses are again positioned to be the first to spot and stop the spread of a contagious disease.

In researching my new book on the battle against infant and child mortality, I’ve learned about the social reformers at the beginning of the 20th century, who brought down the high rates of infant mortality in New York’s tenements, where poor families, many of them recent immigrants, lived crowded together, without health care. In that effort, as in the work done with older children in the schools, nurses were on the front lines.

School nursing in the United States began in New York City in 1902. Dr. S. Josephine Baker, the pioneering physician who was the first director of the New York City Bureau of Child Hygiene — the first such bureau in the United States — wrote in her 1939 autobiography, “Fighting For Life, that when she and other doctors did medical inspections in the city schools at the turn of the century, “We started out on the principle that any case of contagious eye or skin disease must be sent home at once to prevent the spread of any further infection. But the sheer numbers of such cases put a stop to that scheme before we were well started. We were literally depopulating the schools.”

Lillian Wald, the director of the Henry Street Settlement, which provided social services on the Lower East Side, offered a highly qualified nurse, Lina Rogers, to work in the schools. She was the first public health nurse in the United States, and the first school nurse; she covered four downtown schools, which served 10,000 children. The new approach involved educating families to care for many skin infections, while developing protocols so that children could stay in school safely, without spreading them. For trachoma, the most dangerous of the diseases, special classes and clinics were established.

The 1902 New York City experiment was an immediate success, with 25 nurses covering 100 schools by March, 1903, and was quickly picked up in other cities. Charity Collins, the first African-American school nurse, was appointed in 1911 for the city of Atlanta, where she also established prenatal clinics and an infant welfare center, bringing services to families who otherwise would not have received them under segregation.

“I’m a believer in meeting children and families where they are, and there’s nothing better than meeting kids at school,” said Dr. Daniel Stephens, the deputy commissioner for family and child health at the New York Department of Health and Mental Hygiene.

Dr. Stephens, a pediatrician, said that the job has changed over time, as children with different medical conditions have come to depend on school nurses for care during the school day. “The clinical side has grown increasingly more complex over the past 15 to 20 years,” he said. “It’s vital — kids with chronic disease deserve to be and should be in school.”

In 2000, he said, there were about 10,000 students in New York with daytime medication orders, and now there are over 50,000, representing a steeply increased workload for school nurses — and also reflecting an enlarged skill set and additional training.

“Through the years, we’ve always tackled anything that had to do with children,” said Sharon Braxton, a public health nurse who is a nursing supervisor in the office of school health. “The Bureau of School Health was started because children were not able to come to school.”

School health nurses in previous crises worked in shelters after 9/11, raised the alarm about H1N1 cases and vaccinated children in schools, and worked after Superstorm Sandy to help children transition back into school.

As schools in New York City reopen now in the time of Covid-19, each school building will have a nurse, which was not the case before they closed.

The school nurses of New York City now have a whole new set of protocols, including careful guidelines about what to do if a student becomes ill during the school day with Covid-like symptoms. There are isolation rooms at every school, where they can evaluate sick students. The city has set up a situation room including the Department of Health, the Department of Education, the Department of Buildings, and the Test and Trace Corps.

If a student is identified as having possible Covid symptoms and sent home, Dr. Stephens said, the health department can verify whether a test is actually positive, and the tracers can reach out to see if there are close contacts and reach back to the principal to provide letters for the community.

This will support the school nurses, he said, “so they can do their job, which is complex.” They are also still responsible for caring for the children with all the regular problems. “The A.D.H.D. children still receive their medication; for the allergic and anaphylactic children, the EpiPen is there,” Ms. Braxton said.

School nurses often connect children to other services, Dr. Stephens said, because “people talk to the nurse,” and with all the emotional challenges facing children and families during the pandemic, from isolation to grief to economic stress, that takes on even more importance. Ms. Braxton told the story of a school nurse who had a child come in last week for an asthma treatment, only to start crying and say, “I lost my grandma, remember we used to always talk about my grandma all the time.”

Ms. Brown said that there are ways to channel the loss and grief to protect everyone, by “learning to love more, honoring our time together, and at the same time, to look at people and say, your mask is not on the right way — you want people to hear you, you don’t want people to disregard what you’re saying.”

“There’s parent anxiety, there will be parent and staff and teacher anxiety,” said Dr. Julia Potter, a pediatrician at Boston Medical Center who is the medical director of the school-based health centers for the Boston Public Health Commission. “The nurses have to straddle both worlds, they’re living it and feeling it, and they have to respond, use science — they’ve been turned into experts overnight in their schools, which is a hard position to be in.”

“Nurses on school campuses end up being the point people for everyone, everyone asks them questions,” Dr. Stephens said. They need all the latest information, and they need backup. “I often find that school nurses are the best way to show what the health department does — our best ambassadors.”

“The children that came in this past week, they checked in with the nurse,” Ms. Braxton said. “They really are so happy to see their nurse, and their nurses are happy to see them.”