A Berkshire school has been hit by arsonists for the third time in three days.
The most recent fire at Slough's Wexham School caused damage put at £100,000.
Police are treating Sunday night's incident, during which a wheelie bin was pulled onto the school's roof and set alight, as suspected arson.
The attacks have left two classrooms in the modern languages block of the comprehensive school in Norway Drive out of action.
It took more than 40 firefighters to bring Sunday's fire under control.
Police are appealing for anyone who might have seen anything suspicious at around 2000 GMT to come forward.