Four fire engines and 21 firefighters and officers were called to a fire at a school in Portobello Road, Kensington.
The fire was in a computer suite in the three-storey building and a small part of the second floor was damaged.
Watch Manager Thomas Wolfe, who was at the scene, said: “When we arrived the smoke that was coming out was very black and thick so we were quite worried about back draught conditions.
“The fire had caught the wall and some of the computers alight but crews worked quickly to bring the fire under control and stop it spreading to other parts of the building.”
The Brigade was called at 2023 and the fire was under control at 2153. Fire crews from Kensington, North Kensington and Paddington fire stations attended the scene.
The cause of the fire was accidental and believed to be caused by a fault within a chilling unit.