At 7.48pm on Tuesday, police received a report of an intruder alarm being triggered at Ash Green Primary School in Clough Lane, Mixenden.
Officers were dispatched to the scene and found one of the buildings on fire, police said.
Emergency services attended - including 10 fire engines - and a male was located.
He was arrested and taken to hospital for further treatment, police confirmed.
Officers remain at the scene of the fire, which is being treated as suspicious at this time.
Information can also be reported anonymously to the independent charity Crimestoppers on 0800 555111 or online.