Students and teachers at hundreds of Toronto schools without air conditioning sweltered their way through record-breaking heat on Wednesday, as the city’s largest school board said it understood why some parents might choose to keep their children at home.

Forecasts said the city might hit a high of 32 C, but the mercury topped 33.9 C at Pearson International Airport by mid-afternoon. With the humidity, it felt like it was in the low 40s. The scorching temperatures beat a 73-year-old record for Sept. 5, set back in 1945 when Toronto hit 31.7 C.

With high humidity amplifying the heat, conditions were unbearable enough to have some people spending as little time as possible outdoors.

That strategy works when staying indoors provides access to air conditioning and other cooling comforts. When those amenities aren’t present – as is the case in nearly 80 per cent of Toronto District School Board schools – being inside can feel even hotter than being outside.

According to the school board, 128 of the TDSB’s 583 schools are fully air conditioned. The hundreds that are not include many of the city’s oldest schools, which were built without modern heat-resistance techniques.

Clinton Street Junior Public School, like many of the board’s schools, does not have full air conditioning. Parent Kelly Johnson says her son came home from school Tuesday – when temperatures topped out at 25 C – with a “bright red” face and hair stuck to his head by sweat.

“He told me that when he was filling something out … sweat was dripping so badly onto his page that it got wet,” she told CTV Toronto.

Johnson said she planned to pull her son out of class on Wednesday.

“I can’t risk having my son in a classroom where the temperature is expected to be (that hot),” she said.

School Board spokesperson Ryan Bird said the TDSB had received a number of phone calls and social media messages complaining about the heat in certain schools.

Acknowledging that conditions were “very uncomfortable” in some schools on Wednesday, Bird said the school administrators were “trying to do [their] best under very difficult circumstances” by opening windows, turning off lights and using fans. Cooling centres had been set up in the gyms or libraries of schools without full air conditioning.

Bird likened extreme heat to snowstorms, saying parents should exercise discretion and do what they think is best for their child during adverse weather conditions.

“If parents don’t want to send their children in, we understand that,” he told CTV Toronto. “On extreme days like this, we get it.”

The school board estimates the cost of installing full air conditioning at all of its schools to be nearly $750 million.

“With a $4-billion repair backlog … to spend hundreds of millions to install full-building air conditioning at the rest of our schools just isn’t in the cards,” Bird said.

The Ontario NDP tried to seize on the issue Wednesday morning, with education critic Marit Stiles holding a press conference outside Clinton Street Junior Public School. She called on the province’s Progressive Conservative government to give the school board money to address infrastructure repairs.

“We would not expect ourselves to work in these conditions inside buildings. We should not expect our teachers and our students to have to learn in this environment,” he said.

Temperatures in Toronto were expected to decrease significantly after Wednesday, with highs in the mid-20s forecast for Thursday and Friday.

With a report from CTV Toronto’s Janice Golding