C.D.C. officials say most available evidence indicates schools can be safe if precautions are taken on campus and in the community.

During the fall term, about one-quarter of school districts were completely online, about half were using a hybrid model, and fewer than one-quarter were fully open for in-person teaching. Yet more than half of school districts had students participating in sports programs.

In an opinion column in USA Today earlier this week, Randi Weingarten, the president of the American Federation of Teachers, and Dr. Rajiv Shah, president of the Rockefeller Foundation, called for widespread testing to keep schools safe and get children back into the classroom, not only for educational reasons, but to restore free school meals, give children a social outlet, and provide myriad school-based services that are vital to low-income children.

The Covid-19 School Response Dashboard, a collaboration that tracks infections in school districts willing to share data, has reported that infection case rates among staff in October and November were similar to case rates in the surrounding communities. More recently, however, staff case rates in New York increased at a faster rate than community case rates.

The causes are not clear. The increases may reflect a more frequent testing of schoolteachers. Case rates increased among teachers engaged in in-person teaching and among those teaching remotely, suggesting in-person instruction was not the sole factor.

Emily Oster, a professor of economics and public policy at Brown University who created the dashboard, said that low case rates in the community make it possible to keep schools running safely.

“Prioritizing schools is going to mean limiting some of those other activities, and deciding that we want to undertake some of those sacrifices to keep schools open, because we’ve decided as a society that schools are important relative to other things,” Dr. Oster said.

“The frustration for many people is that you can go to an indoor restaurant. In Massachusetts, I could go to an indoor water park like Great Wolf Lodge — I can take my kids to Great Wolf Lodge. But in a lot of places in Massachusetts, there has been no school.”