Four teenagers have been arrested in connection with the fire at the Darul Uloom School in Chislehurst, south-east London on Saturday night, Scotland Yard said.
Two 17-year-olds and two 18-year-old were arrested on suspicion of arson late yesterday and taken into custody.
Bromley Borough police officers are continuing to establish the full circumstances of the fire.
More than 100 pupils and staff at the Islamic boarding school had to be evacuated when the fire broke out.
More top news
Tens of thousands of people have travelled to a sleepy town in the American west, to witness a rare celestial event.
Warming up over the next few days. Mostly dry in the south, rain at times in the north.
A petition for a statue of rapper Missy Elliott to replace a Confederate monument in Virginia has been signed by more than 15,000 people.