ORANGEVILLE, ONT. -- Select health units across Ontario are making the call to close schools and opt for remote learning.

School boards in Peel Region, Toronto and now Wellington-Dufferin-Guelph have shifted temporarily to online learning while the Ontario government maintains classrooms are safe.

Teachers in the Upper Grand District School Board prepared students to return to virtual learning starting Wednesday.

Wellington-Dufferin-Guelph's medical officer of health, Dr. Nicola Mercer, said she issued the order for schools to close Monday night after seeing data from the past six days.

"We've had nearly 300 cases since Thursday. We closed more classrooms in one day than we did at any time in the pandemic. What we saw, also, was our seven-day rate of cases quadrupled," Mercer said.

Health officials in Toronto and Peel reported similar issues.

The president of the Simcoe County Elementary Teachers' Federation said the province should have closed classrooms. "Just as a precaution to ensure there wasn't any spike in the number of cases and to keep students and staff safe," said Janet Bigham.

Schools across Simcoe Muskoka remain open. The Simcoe Muskoka District Health Unit logged nearly 400 COVID-19 cases over the Easter long weekend and confirmed four active outbreaks in schools in Bradford, Barrie and Alliston.

The Ontario government implemented a 28-day province-wide shutdown Saturday to curb the worsening third wave driven by highly contagious variants of concern but chose to keep schools open.

Premier Doug Ford said Tuesday students needed to be in class for their mental health and added that infections happen in hot spot communities, not schools. "When the kids go back into the community, that's where it's happening. It's not happening in the schools. It's happening when there's community spread in hot areas," he said.

The public health order issued in Wellington-Dufferin-Guelph remains in effect until at least April 19.

With files from The Canadian Press