Doherty High School in Colorado Springs is closed today.
District 11 says it's because of an "isolated incident that caused heavy smoke in the building."
A district spokesperson says a kiln was left turned on in the art room, which caused a piece of wood to smolder and fill the building with smoke.
The district says the building wasn't damaged, but there are ventilation issues.
Students who are already at school will be dismissed early. Bused students will be picked up and taken home.
Classes will resume on Friday.