FLAMES licked the roof and window frames at The Chase High School, in Malvern, on Wednesday night after a fire started in a wheelie bin.
A police officer on patrol spotted the blaze in the bin close to the building at 8.30pm and raised the alarm.
Firefighters from Malvern's White Watch arrived in time to prevent serious damage to the school.
"We had to cut away a bit of the roof and a few of the windows were cracked," said Firefighter Keith Massam.
"It was easily dealt with and we had it sorted in half an hour, but it could have been far worse. We got there just in time."
Police spokesman Vicki Davies said the incident was being treated as arson.
"A window had been smashed and there was a fair bit of vandalism. Eggs had been thrown about," she said.
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