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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It will be another misty and cloudy start to the day.
Another rather cloudy day, with the easterly wind continuing to bring low cloud in from the North Sea.
Some mist and hill fog tonight. Brightening up on Thursday.