Oklahoma City firefighters went to school Saturday night and taught one fire a quick lesson.
About 8:30 p.m., fire crews were called to the old John Marshall High School, 9017 N University. They saw flames shooting from second-story classroom windows.
The fire was extinguished in about 20 minutes. Department officials said they were not immediately sure what caused the fire.
Arson investigators were called to investigate because there were no working utilities running to the building and all the classrooms were empty.
An estimate of the damage was not available.