Over half of U.S. public elementary and secondary school students will study online this fall, according to new research.

In addition to the 52% of students learning online, 44% will attend school in person on partial schedules, such as rotating days. Four percent of school districts remain undecided, according to a survey by Burbio, a data service that aggregates school calendars nationwide.

“We have seen a dramatic shift to online-only learning in the past three weeks,” Julie Roche, Burbio co-founder, said in a press release. “Large districts such as Chicago, and Sun Belt cities such as Houston and Miami, along with large suburban districts such as Fairfax County, Virginia, were all setting plans to return with in-person learning and shifted to fully remote.”

The 200 largest districts are 66% virtual, Burbio stated.

But the largest school district in the U.S. — New York City — recently announced it would have students attend school in person.

In the Northeast U.S., districts that will hold online classes only are mixed with districts where students will attend class in person. Along the West Coast, most districts will be online, while the Midwest looks predominantly in person or hybrid, according to Burbio’s map of school districts across the country.

Twenty-five percent of schools have stated they will hold classes every day. Other schools that plan to hold classes in person include hybrid formats in which 19% of students attend some but not all days of the school week.

“We expect this situation to stay fluid for the entire academic year and we will continue to measure it,” said Roche. “Many districts have thresholds for COVID-19 levels that could result in converting back to remote learning. Other districts are planning to revisit the online decision as soon as September and could convert to in-person models.”