Several Ontario school boards are looking to keep COVID-19 safety protocols such as masks in schools longer than the provincial government's March 21 end date, but the education minister signalled that may not be possible.

Toronto District School Board trustees voted during a meeting Thursday night to write a letter to the chief medical officer of health, the Ministry of Education, and Toronto Public Health to request additional time for removing public health measures in TDSB schools.

The trustees asked for a response by Wednesday, but a statement Friday from Education Minister Stephen Lecce suggested those types of requests won't be entertained.

"School boards in this province are expected to implement this cautious plan, coupled with the ongoing improvement of air ventilation within Ontario classrooms," he wrote.

Beyond the province's March 21 timeline, masking will still be "strongly encouraged," the TDSB said Friday in a letter to parents.

"For the past two years, the TDSB has prioritized the health and safety of students, staff and school communities," the board wrote.

"As we move to a more sustainable, long-term approach to managing COVID-19, you are encouraged to continue with the layers of protection that make you feel comfortable."

Other measures such as cohorting and physical distancing are set to end on March 21, while staff vaccination policies are being lifted for school boards across Ontario as of Monday.

The province had already stopped tracking COVID-19 in schools, and the TDSB said Friday that its additional measure of sending positive case notification letters to affected classrooms would continue to the end of March and then will be "reassessed."

Instead of providing data on individual cases in schools, the province has been reporting the number of schools closed due to COVID-19 operational reasons - none were listed as of Friday - and the percentage of staff and student absences. The Toronto Catholic District School Board said in a note to parents Friday that the province would stop collecting absence data after April 14.

The Catholic board said they voted to ask the ministry to let them keep mask rules in their schools for two weeks after March break, which begins Monday, to allow for more time for younger students to get vaccinated.

But the letter to parents said that following provincial direction, on March 21 masks will no longer be mandatory, cohorting and distancing won't be required, limits on assemblies and events are removed, and staff and students won't have to confirm that they have self-screened for COVID-19 symptoms.

In Guelph, the Upper Grand District School Board said mandatory masking will end in its schools on March 21, as the board doesn't have the authority to extend those rules after the province lifts mask requirements.

"We know that the topic of masks can be a divisive one," the board said in a statement on its website.

"We want to stress that students, staff and visitors are still welcome to wear masks in our schools, and this is their choice. Masking indoors continues to be strongly encouraged."

Ontario announced this week that on March 21, masking requirements in most settings will be removed – including in schools and child-care settings.

A coalition of children's hospitals had urged the province to keep masks in schools for at least two weeks after March break, saying that public health measures are what have kept schools open.