The union representing public school elementary teachers says the late September heat wave across Southern Ontario made conditions in many classrooms "unbearable".
The Elementary Teachers' Federation of Ontario is calling on the province to take steps, which could include installing air conditioning or cooling stations in schools.
"Students not being able to concentrate, very lethargic, very tired," says ETFO local President Adelina Cecchin. "Teachers feeling very exhausted. Some are even going home. Some are saying, "I've got extreme headaches because of the heat". We're hearing the same things from students. So it's definitely having an impact on our students and on our teachers."
Cecchin says climate change is a real problem.
"This climate issue is not going to go away and if we're really there to try and make sure that our students are learning we have to get this heat condition under control. Then we need to start to look at funding to be able to address this because if we're going to really look at this in a realistic way, we do need to start bringing air conditioning into our schools."
She says students and staff shouldn't be put in that position,
"You can imagine, already with the heat that's outside, add to that the humidity, you've got a class of 30 students coming in, maybe from outside recess where they've been dealing with the hard top outside that has been heated by the sun, it makes for very difficult learning conditions in the classroom."
Cecchin says, during the heat wave, staff and students were urged to not overexert themselves, to stay hydrated and to close the blinds and keep the lights off.
Temperatures are expected to start to drop tonight with a forecasted to hover around 11C.