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
Jessica Urbano Ramirez was two weeks away from her 13th birthday when she died in the June 14 blaze.
No-one was on board the single-decker vehicle, Humberside Police said.
The disgraced film producer has been the subject of an investigation in the US into allegations that he sexually assaulted numerous women.