The alarm was raised after the device was brought to the primary school in Scalloway, Shetland, at around 11:45am on Friday.
Police said Shetland Coast Guard and Shetland Council are assisting on the scene, and Explosive Ordnance Disposal was also called in to assist.
A police cordon has been established in the building, with investigations ongoing.
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A policeman Scotland The spokesperson said: “Police and emergency services are currently at a primary school in Scalloway, Shetland, after a historic munition was found on a local beach and brought to the school at around 11:45am on Friday May 26, 2023.
“A cordon has been placed around the area and the school has been evacuated as a precautionary measure.
“Shetland Coast Guard and Shetland Council are helping.
“Explosive Ordnance Disposal has been informed and will attend. The investigations continue.”