Five fire engines tackled the blaze on the ground floor of the Periton Mead School building.
They were called to the incident at 9.51pm.
The blaze, which was thought to be deliberate, destroyed 50 per cent of the building.
“On arrival at the scene fire crews confirmed a derelict property well alight and requested an additional three fire appliances which were mobilised from Porlock and Williton,” said a spokesperson from Devon and Somerset Fire and Rescue.
“The water carrier from Bridgwater also attended.
“The incident involved a two storey derelict building formerly used as a school and gym.
“Crews extinguished the fire using two main jets, one hosereel jet and thermal image cameras to check for hotspots.
“The cause of the fire was believed to be deliberate and police also attended.”