Around 40 volunteer firefighters from McMasterville and surrounding towns worked throughout the early hours to douse the flames at La Farandole school, built in the 1950s.
Fire department officials say the fire, which started around midnight, likely began with a picnic table beside the school.
Flames from the burning table spread to the school and up to the roof, which became engulfed in flames.
“The flames were considerable and it was difficult to get into the building,” said David Roy, captain of the McMasterville Fire Department.
Marie-Rose Vandemoortele, an official with the Patriotes school commission, said the kindergarten to grade six school served around 200 students.
“It’s devastating,” she told Radio-Canada.
The school was an important part of the community, Vandermoortele said.
“Our priority is to ensure the building is safe and to relocate the students for August,” she said.