Toronto's public health agency is calling on the local public school board to reduce class sizes in September, suggesting the province's back-to-school plan doesn't go far enough to prevent the spread of COVID-19.

In a letter to the Toronto District School Board, associate medical officer of health Dr. Vinita Dubey said Toronto Public Health is worried about the risk of COVID-19 spreading if class sizes remain the same.

"In elementary classes (junior kindergarten to Grade 3) where masks are not required, smaller class sizes will particularly be important to ensure students can be spaced out to reduce transmission," Dubey wrote.

She said teachers will also be able to better control classes and prevent crowding in hallways if class sizes are reduced.

And importantly, she said, reducing class sizes will make physical distancing easier.

"Scientifically, it has been shown that keeping a distance of two metres from others works well to prevent the spread of respiratory droplets from one person to another," she wrote, noting that desks should be spaced out accordingly.

Toronto Public Health did not respond to a request for further comment on Friday.

In a written statement, TDSB spokesman Ryan Bird said the board has been working with the public health agency since the beginning of the pandemic and has incorporated many of its suggestions.

He said the board has also been speaking with the Ministry of Education about how it could lower class sizes, but that option may not be economically feasible for all schools.

"Other strategies may have to be considered, such as shortening the school day, reassigning teachers from non-classroom roles and lowering class sizes only in areas deemed at risk by Toronto Public Health," Bird said.

He noted funding provided by the province wouldn't cover the costs of hiring enough teachers to reduce classes in the TDSB, "let alone the entire province."

Ontario's school reopening plan, which was released last week, does not mandate the reduction of class sizes for students from kindergarten to Grade 8, but says they should be prevented from interacting with peers in other classes.

High school class sizes in all but two dozen school boards are to remain the same as well.

In those 24 boards — the TDSB among them — high schoolers will attend class only half the time in cohorts of 15. The rest of the time, they'll do school work remotely.

Parents can also choose to keep their kids out of school and have them learn at home.

Premier Doug Ford and Education Minister Stephen Lecce have spent much of the past week fending off critics of the plan who argue it is underfunded and unsafe.

The Opposition NDP and the province's four major teachers' unions have said they feel students should be in class full time, but with reduced class sizes. They also argue that $309 million in new funding doesn't go far enough to make that happen.

Of that money, $30 million is earmarked to hire more educators — a figure opponents say is too low.

On Friday, Ford argued against mandating smaller class sizes across the province, noting the case load is different in different regions.

"One size doesn't fit all," he said during his daily news conference.

Ford's comments came the same day that the Public Health Agency of Canada released its own guidance for reopening schools across the country.

The document outlines general best practices for staff and students, including promoting physical distancing where possible and mandating mask use for those over the age of 10. The document also suggests that schools consider reducing class sizes, if it's feasible.

In issuing the guidance, chief medical officer Dr. Theresa Tam cautioned schools to also consider "local epidemiology" when crafting their own reopening plans.

"This guidance document should be used alongside guidance from provincial and territorial health authorities, ministries of education and Indigenous community governance structures," she said.

This report by The Canadian Press was first published Aug. 7, 2020.

Nicole Thompson, The Canadian Press