The School District of Philadelphia officials say they immediately investigated after receiving a report on Wednesday about the mold situation.
They say the mold issue is due to heating, ventilation and air-conditioning (HVAC) issues and condensation damage which caused the mold in several classrooms.
The workers began to remove the problem at 3:30 p.m. on Wednesday. At this moment roughly 80% of the remediation has been completed.
However, school officials say the school will remain closed until the building is 100% free of the mold problem.
Earlier, several parents expressed their opinions outside.
"I think that's disgusting. There's no reason they're not keeping up on their maintenance when it comes to that," parent Shaqueia Johnson said.
Some families hadn't heard that classes were canceled until they arrived to drop off their children.
"I'm just upset. I have to go to work and I don't know if daycare will take him," parent Shaneea Baker said.
Parents are worried about the health implications - how long the mold has been there and if it's all gone.
"My son has asthma and I know that's going to affect him," Baker said.
"We are checking all of the rooms, we have about 41 rooms in building; we are checking all of those. We have common spaces, hallways, bathrooms. We are doing a complete check of the building," Lee Whack of the School District said.
"We understand that parents are concerned and we are concerned as well. We are focused on getting to the bottom of this issue," Whack said.
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