Police say arsonists caused £2,000 worth of damage at a Cuckfield school.
Five wheeled bins worth about £250 were set on fire at Warden Park School.
The blaze spread, damaging walls, Tarmac, a window and a security light.
PC Geoff Bennett said: "If anyone heard or saw anything suspicious in or around the schools in the early hours on Sunday morning or on Saturday evening we would ask them to contact us."
Police said they were treating the attack, which happened at 2am on Sunday, as arson.
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