Five children were arrested after a fire destroyed a school which was due to reopen after the summer holidays.
Leyland St Mary's Catholic Technology College in Royal Avenue, Leyland, Lancashire, was devastated by the blaze, which broke out shortly after 4pm on Sunday.
Five boys aged between 11 and 15 have been released on police bail after being held on suspicion of arson, Lancashire Police said.
Lancashire Fire and Rescue Service said 125 firefighters and 20 engines were involved in tackling the blaze.
The school, which was built in 1957, had no sprinklers. The cause of the blaze is being investigated but is believed to be suspicious, the fire service said.
About 10 fire engines remained at the scene in the early hours of today to extinguish the last pockets of flames and ensure the scene was safe.
Staff were due to attend the school today for an inset day, its website said, and pupils were to return for lessons after the holidays tomorrow.
A statement on the website said the fire had caused "devastating damage" and asked people to "please pray for the school at this difficult time".
The five boys, from Leyland, have been released until September 30 pending further inquiries.