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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Des Coleman has the latest forecast for the West Midlands
Des Coleman has the latest weather forecast for the East Midlands.
Des Coleman has the latest forecast for the West Midlands.