Carl Williams, Headteacher at Moreton School in Wolverhampton, has described an incident in which 20 pupils were jabbed with a diabetic testing needle as "frightening".
Some of the children have been taken to hospital for hepatitis jabs as a precaution.
An 11-year-old boy has been arrested.
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Old Market Square in Nottingham was a blaze of orange, green and white as hundreds brave the blizzard-like conditions.
Snow showers to continue with bitterly cold conditions across the region.
Bitterly cold and windy with snow showers, sometimes heavy.