It was around 10:40 a.m. when firefighters were called to Glasgow High School, which is located at 1901 South College Avenue in Newark.
Arriving crews found a small fire in a second floor bathroom, which was quickly placed under control.
State fire marshals were called to the scene and investigators determined the fire was intentionally set.
All students were evacuated in an orderly fashion. No one was injured.
Authorities say damage is estimated at approximately $5,000.