Some parents and researchers say some policies put in place early don’t match the data emerging on how slowly the coronavirus spreads among schoolchildren. They argue for new policies that let schools stay open with mask-wearing and social distancing while limiting quarantines and allowing districts more flexibility to design their own responses.

“There’s been a tremendous failure of data on this,” said Brown University economist Emily Oster, who has studied Covid-19 and schools and said authorities often overreacted to the few cases that appeared in schools. In early September, she organized a team of data scientists to track confirmed cases in schools across the country.

The effort, which has grown to track more than 9,000 schools and more than four million students doing in-person learning nationwide, found a biweekly infection rate of 0.22% among students and 0.42% among staff as of early November. The rate equates to 1.1 children and 2.1 staffers infected per 1,000 each week. The project’s preliminary results indicate that nationwide, students who attend school are infected at a rate that is 27% lower than the case rate of communities they live in.

“They can quarantine 500 people, and that’s really costly on a lot of levels, and zero of them end up having Covid,” said Ms. Oster, who believes public officials should reconsider school quarantine policies, “and then you say, ‘OK, it seems like the other mitigation strategies we were taking were actually working pretty well.’ ”