A new notification is posted nearly every day on the D.C. school system’s public website. They trickle in a few at a time.

“A letter to the Miner Elementary community was sent on April 2, 2021, notifying them of a positive COVID-19 case in the building when students were present on April 2, 2021,” a recent notice says.

The school system has posted about 100 notices since schools reopened for in-person learning in February, bringing back about 20 percent of the school system’s population. Each posting could mean that at least one classroom — up to 12 people — has to switch to remote learning and quarantine for two weeks.

The notices can be concerning, but city officials say they are more reflective of students bringing the virus into schools rather than the virus spreading in schools. School system officials say that when multiple people in the school test positive, they are usually siblings in different classrooms at the school.

They also said they are not aware of any instance in which a classroom was sent home to quarantine and then one of those students or staff members or one of their close contacts tested positive, suggesting that the infected student did not spread the virus in school.

Though that promising data point is hard to prove since it relies on families self-reporting any positive cases during quarantine, school system officials say they believe their efforts to stop the spread of the virus in schools are working. A charter school had one positive case after a cohort was quarantined, and private schools had five instances, according to data provided by the city.

“We are confident that our mitigation strategies are working,” said Elizabeth Bartolomeo, spokeswoman for the D.C. school system.

Unlike some other jurisdictions, the city does not have a tracker that shows when and how many cases are detected at each school. And looking at the city’s youth infection rates doesn’t say much about schools since most students are still learning virtually and many of the ones who do attend in-person classes are still virtual most days.

This week, the city began posting data showing schools with the highest number of cases. The Friendship network’s Armstrong campus in Northwest Washington had 19, all among staff. The network said the Armstrong campus had been used as a testing site until December and conducted a total of 3,500 staff tests, with 24 coming back positive.

Six of the nine schools with the highest number of cases are private schools.

According to city data, the number of youth infections spiked in January after the holidays and before most public schools started offering substantial in-person learning. The number of infections are far higher than they were last summer, though that could be because coronavirus tests for children are now more accessible.

City data shows that just 224 of the 4,400 cases in children 18 and younger between Aug. 1 and March 25 have been connected to schools, according to Ryan Stahlin, a data scientist who started an independent website tracking the city’s coronavirus cases. (School numbers rely on private, charter and the public school system reporting positive cases to D.C. Health.)

A public information request for more information on school-by-school cases was turned down.

“To me, it seems pretty clear that there is significant community spread not related to schools in that age group,” Stahlin said.

Based on the information that is available and data city leaders have provided, there is no indication that there has been substantial spread in school.

The city has enacted cohorting and quarantine measures in schools, some of which are more conservative than guidance from the Centers for Disease Control and Prevention. For example, the public school system does not allow middle and high school students to switch classes and switch cohorts even though national guidance — and more recently amended local guidance — allow for it.

The city has followed a six-foot social distancing rule in schools but will soon switch to three feet following revised CDC guidance. Currently, anyone in a cohort with a positive case must quarantine for 14 days, but the school system will shorten that to 10 days later this month.

Numerous studies have attempted to assess the risk of reopening schools in the pandemic. A recent CDC study found that schools could safely reopen with protocols in place, including improved classroom ventilation, social distancing and mask mandates. The higher the community spread is, the more precautions are needed.

The District has a program aimed at testing a random sampling of 10 percent of students at each school each week. Originally, the school system tested any student who wanted to be tested every other week but attendance and staffing problems hampered the effort.

In all, the city has tested 8,854 asymptomatic public school students in the traditional public school system and charter students since early November, and 68 have come back positive.

Staff members, who have been on campus longer than students and only started to become fully vaccinated in March, account for more than 60 percent of the school-related cases. Most staff members have been vaccinated, and the city started testing public school staff regularly on campus, even if they are vaccinated.

Additionally, more than half of cases connected to students and schools are self-reported.

The two largest charter networks — Friendship and KIPP DC, which collectively educate more than 11,000 students across more than a dozen campuses — opted out of the city’s testing program and implemented their own.

KIPP DC does pooled testing. That means it processes an entire cohort’s coronavirus tests at once to determine if anyone in that cohort is positive. One positive result means the entire cohort quarantines.

During the week of March 22, KIPP DC had 1,207 students in its buildings and conducted 156 pool tests, which represents 156 classrooms. Of those, five pool tests came back positive, resulting in five classes going back to remote learning during a quarantine period. Last week, the school conducted 151 pool tests and zero came back positive.

Adam Rupe, spokesman for KIPP DC, said the network has a rigorous symptom-screening process. Before a student enters the building, the family needs to fill out an electronic form that asks if they have experienced any coronavirus symptoms or if they have come in close contact with anyone who has tested positive or has a pending test. Each day, he said, based on the family’s information, at least one student has to stay home until they receive a negative test or quarantine for two weeks.

“When we’re looking at the numbers, we are really happy that we are below the city average and we are also paying close attention to the Ward 7 and 8 rates,” Rupe said.

Friendship said it has conducted 1,055 student tests since March and has detected zero positive tests.

Some private schools, most of which are located in neighborhoods with low infection rates, also provided data to The Washington Post.

Washington International School said it has processed 6,200 student swabs and 2,700 adult swabs through its pooled testing program between Nov. 30 and March 31. One asymptomatic faculty member has tested positive and one student tested positive. Others have self-reported positive cases. The school remained virtual for more than a week after winter break and expected all families to follow city health guidelines and self-quarantine if they traveled for the holidays.

The school has had instances where people have called in and self-reported that they contracted the virus.