Four fire engines and around 25 firefighters were called to a fire at a school on Bath Road in Hounslow.
Part of a classroom in a single-storey block was damaged by fire. Around 1400 children and staff left the building before the Brigade arrived. There were no reports of any injuries.
The Brigade was called at 0904 and the fire was under control by 1052. Fire crews from Heston and Feltham fire stations attended the scene.
The fire is believed to have been caused by an electrical fault in a light fitting.