ABOUT 35 firefighters battled a blaze at Rockingham Senior High School on last night.
It is estimated the classroom fire caused about $100,000 damage.
A Department of Fire and Emergency Services spokeswoman said they were notified of the fire at 7.47pm by a member of the public, who said there was an area near an air conditioning unit on fire.
Seven fire crews from Rockingham, Kwinana and Hope Valley attended and had the fire under control by 8.25pm.
The cause of the fire was deemed accidental.