An 11-year-old schoolboy has been arrested after at least 20 of his classmates were "jabbed" with the tip of a diabetic needle.
West Midlands Police said no one was seriously hurt after being stabbed by several finger-prick pens brought into Wolverhampton's Moreton Community School by a Year Seven student.
Pupils at the school have been advised to have precautionary injections to guard against possible hepatitis, although health experts have said the risk of any infection is minimal.
A police spokesman said officers launched an investigation on Monday after receiving three reports from parents saying their children had been "jabbed" with the pen whilst at school.
Sergeant Steve Perry, of Low Hill police, said: "Officers have been into the school and identified at least 20 children it's believed were jabbed with the pen.
"It has a needle 'nib' just 3mm in length so none of the children are seriously hurt and public health officials have advised that the chance of infection is negligible.
"However, the pupils have been advised to have hepatitis injections as a precaution.
"An 11-year-old boy was arrested from his home address in Low Hill yesterday morning and having been questioned by police has been bailed until a date July pending further inquiries."
In a letter to parents, the school's headteacher, Carl Williams said: "Naturally, this is a very serious incident, and we would first like to take this opportunity to apologise for any injury your child may have sustained and the concern you must be feeling for your child's health and safety.
"I would like to assure you that we take the health and well-being of all our students very seriously and have acted quickly, liaising with both public health experts and police concerning this incident. Mr Williams said the school believed that the needles used were clean, and was treating the incident with the gravity it required."