Five fire engines and around 35 firefighters were called to a fire at a school on Balmoral Road, Worcester Park.
A small part of the loft space was damaged by fire. The alarm was raised by a fire alarm sounding within the roof void.
Approximately 300 pupils and 50 members of staff were evacuated to another school building as a precaution. There were no reports of any injuries.
The Brigade was called at 1322 and the fire was under control at 1440. Fire crews from New Malden, Sutton, Mitcham and Surbiton fire stations attended the scene.
The fire is believed to be accidental and caused by hot works being carried out on the roof.