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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Derbyshire paceman Mark Footitt is named in England's squad for fourth Ashes Test.
East Midlands weather: Sunny spells but cloudy with rain at times later.
West Midlands weather: Some rain today, but showers clearing.