DETROIT — Kenneth Chapman Sr. was hopeful as he navigated a hulking Detroit Public Schools van down the street, pulling up to a brick home. Out front, there were signs that the girl he was looking for lived inside. Amid the discarded plastic cups in the yard, there was a ball, and on the porch a small bike, painted fluorescent pink.

“Normally when I get to the house and I see toys or bikes, I think, ‘Okay, somebody’s going to be here,’ ” Chapman said.

But when he knocked, no one appeared.

This was one of the two dozen stops Chapman, who works in the school system’s Family and Community Engagement Office, would make, looking on this chilly day in late October for students who had been missing classes. Some of the children on the list had worrisome numbers of absences this early on in the school year. But there were 3,000 students the district could not account for at all.

School districts across the country that closed buildings in mid-March in response to the coronavirus pandemic handled the transition to remote learning with varying levels of success. During the disruption, schools lost track of students. Many students who were present in the classroom in early March could not be found online. And others who showed up in the spring haven’t been seen since.

Even before the pandemic, districts had to track down children who had stopped showing up to school or had failed to appear for a new school year. They have strong incentives to find them; school funding is often allocated on a per-pupil basis. Sometimes it turns out students have moved and enrolled in other districts. Other times they can’t be found and are removed from the rolls.

But this year, students have disappeared from classes in unprecedented numbers, forcing districts to rethink their approach to those who stop showing up. Many districts, cognizant of the damage that lost school time can cause, have employed extraordinary efforts to track down students to ensure that they are safe and have devices to learn. Others, like Detroit and Miami, have kept students on rosters even after they failed to show for an entire month. North Dakota began tracking attendance for all schools on a daily basis, and several schools used coronavirus aid to hire family liaisons to find missing students.

Several states have seen precipitous drops in public school enrollment this school year, and many have seen a rise in the number of students enrolled in private schools or being home-schooled. In addition, the children who would have started preschool or kindergarten in the fall are staying home in droves, as those grades are not mandatory in most states. But there’s another category of students: those who were supposed to be in classes this year but still have not appeared.

In North Carolina, a state education official told state lawmakers in December that more than 10,000 students had not been accounted for. New Mexico could not account for more than 12,000 students at the start of the school year, children who were enrolled before the pandemic but never showed up in the fall. This month, the state’s education department reported that more than 2,700 students were still missing.

Katarina Sandoval, New Mexico’s deputy secretary of academic engagement and student success, said that in previous years, the number of students who failed to come to school was so small that they did not even have a name for them. Many of them were high school dropouts.

But this year, the missing students come from all grades. The state organized an effort to reach out to families and enlisted the help of social service agencies to support those families who struggled to get their children to school.

A lot of these discrepancies stem from poor record-keeping systems. In many states, districts collect attendance individually and do not have a good way of sharing with one another. So a student who merely transferred may be marked as missing, and a student who cannot be found could be presumed to be in another district.

Detroit, which opened buildings in the fall for optional in-person instruction, had more than 900 students who did not enroll until after October, weeks into the school year. The district, which has long struggled with chronic absenteeism, launched an aggressive attendance initiative in 2019 backed by private foundations that allowed it to hire attendance officers for every school to keep tabs on children who did not show up.

During the pandemic, the district capitalized on the initiative, launching three door-to-door campaigns that sent staff and parent volunteers to the homes of students who have not been showing up to classes — either virtually or in person. In late January, the district was in the midst of its third campaign, with volunteers hitting the streets in 26-degree weather to check on students.

When school districts reach out to families, they often do so through text messages, robocalls, emails, Facebook posts and snail mail. It’s communication that requires families to have a working cellphone, Internet access and a fixed address. That means families who move frequently, change cellphone numbers or do not speak English can be left out of the loop and can be difficult to find.

Sacramento City Unified School District learned that lesson the hard way, when it lost touch with more than 1,600 students after closing in mid-March. None of them had responded to check-in calls from educators, and none of them logged on when virtual classes started a month later.

The district jumped into action, dispatching staff members to students’ homes and setting up a food truck in the middle of large apartment complexes to draw out families and their children. If they found a student, they collected current contact information and ensured that the student had what was needed to log on. When that did not work, the district sought addresses from the state’s food stamp program and from social service agencies. About three-quarters of the district’s schoolchildren qualify for low-cost health insurance, food stamps or other social service programs.

By summer, just 845 students were missing. And by the start of the school year, only nine remained unreachable.

It is deeply worrisome for educators when they cannot account for where a young person is, or whether they are learning and safe. When school is in session and classes are face to face, teachers are better able to detect whether a schoolchild is being abused or neglected. Those check-ins are tougher when school is closed and children are no longer showing up for face-to-face instruction. Educators accounted for about a fifth of child abuse reports in 2018, according to federal data.

“There’s just a whole layer of kids who have just disappeared,” said Hailly T.N. Korman of the think tank Bellwether Education Partners, who is studying what she calls “the attendance crisis.”

She is particularly concerned about children who come from low-income households, English-language learners, homeless students and migrant students, whose families may have been hit especially hard by the economic downturn: “It’s been true for generations . . . that every one of society’s unmet needs of children shows up at a classroom door.

“Now there’s no classroom door to show up at.”

“School has historically been the daily wellness check for a lot of kids,” Korman said. “They don’t have that anymore.”

Like cities across the country, Detroit shut down its schools in mid-March as the pandemic tore through the community.

One of its victims was 5-year-old Skylar Herbert, the daughter of a police officer and a firefighter, and the first child to die of covid-19 in Michigan. Shortly thereafter, Gov. Gretchen Whitmer (D) formed a task force to examine the pandemic’s lopsided effects on communities of color. She dedicated the task force to Skylar, who was Black.

In the fall, the district reopened school buildings but gave parents the option of sending their children back or keeping them home and having them learn online. About a quarter of parents said they would send their children back. The rest either could not be reached or opted for virtual learning.

Last spring, after schools closed, the district endeavored to get a laptop with Internet embedded out to every one of the district’s 50,000 students, raising $23 million in three weeks from Detroit-based companies to fund the effort. They distributed more than 45,000. But many students never showed up to pick up a device — including nearly every child who remained missing deep into the school year. About 70 percent of the students on that list were also considered chronically absent before the pandemic.

Nikolai Vitti, the superintendent of Detroit Public Schools, said the number of students missing from classrooms is staggering. In the spring, only 10 percent of students were engaged with virtual learning, prompting the district to launch an aggressive campaign of door-to-door visits to ensure that families had devices and knew about when the district would open virtually. A month into the school year last fall, 8,000 students were still missing. About 5,000 of them joined the school year late.

“We’ve always had issues with absenteeism because of the impact of poverty,” Vitti said. “But nothing like this.”

That was true for Chena Castigliano, who has been raising three young children on her own since her husband, a drywall installer, was arrested and sent back to his native Mexico last year. Then came postpartum depression and eviction. She registered her school-age children, 5-year-old Emiliana and 6-year-old Emilio, for face-to-face classes in the fall, but they went only sporadically because she struggled to find them transportation. Things got worse when schools shut down in mid-November.

The children had to share a loaner device, and then she could not afford Internet. Because classes are still remote, the children have not attended since early December.

Not all families have “somebody to lean on,” Castigliano said.

On that Friday, some of the families that Chapman encountered had easily resolvable issues that had kept students from virtual classrooms. One high school student had missed Oct. 7 because she had lost her laptop charger — but later recovered it. A boy’s mother explained that he could not log on that day because of an enrollment issue at the school. Many times, Chapman said, students have not logged on because neither they nor their parents could figure out how. In those cases, he and the other staff dispatched to homes become de facto IT specialists.

But other times, the issues are greater. That same week, Chapman had arrived at a home where a cord snaked out the front door to an idling car. The family’s power had been cut, and they were using electricity drawn from the car for the house. It was not uncommon, Chapman said, to come across a family whose children had stopped showing up because there was no electricity in the household.

The most worrisome cases are still the ones where a knock on the door yields no answer, or when the address belongs to an abandoned home.

The attendance crisis will have lifelong consequences for the students who are missing weeks or months of classes or who decide to leave school altogether.

“They might not come back at all. They might not finish high school,” said Korman, the researcher. “They will struggle in the workforce. It will be difficult for them when they raise their own children.”

“We’re going to see the consequences of this for generations.”

Correction: An earlier version of this article incorrectly stated that New Mexico is still searching for 12,000 students. Since the fall, the number has dropped to 2,700 missing.