Classes will be held as scheduled Tuesday at Riverside High School in Windsor, even though a fire damaged the main gymnasium last night.
Officials said lightning may have struck the school at approximately 6:15 p.m.
Firefighters had to tear open parts of the roof to get at the fire and water leaked down on to the gym floor.
"The damage was isolated to the main gymnasium and we'll be able to operate the school quite well without it for the next few days," Greater Essex District School Board spokesperson Scott Scantlebury said.
Gym classes can be held outdoors for the time being, he said.
Firefighters spent about an hour and a half tearing open two sections of the roof of the gym to make sure all the fire was extinguished.
Stephanie Garant was in her kitchen next door to the school when she heard the lightning strike.
"It was a very loud lightening strike. I thought it was in the backyard of my house," she said.
Garant said she went outside and found smoke rising out of the roof. She immediately called the fire department.
Lee Tome, Windsor Fire and Rescue's chief fire prevention officer, confirmed there was lightning in the area at the time the fire started.
Tome said the school suffered "extensive water damage to the gymnasium floor."
Tome ruled the fire is not suspicious but didn't confirm lightning was the cause. He didn't have a damage estimate.
School officials said it will take several days to assess the damage.