A 14-year-old pupil was arrested after he attacked at least 20 pupils with an 8mm medical needle at a school.
The incident, involving what is believed to be a diabetic insulin pen, happened at Toot Hill School in Bingham, Nottingham, on Wednesday.
Parents were informed of the incident and advised to get their children tested for infections, although the risk is low, the school said.
Nottinghamshire Police confirmed they had arrested a 14-year-old boy over an incident involving what is believed to be a diabetic pen at the school on Wednesday but described the injuries suffered by the pupils as "minor".
They refused to confirm reports the children had been taken to hospital.
A statement from the school on its website said: "The incident that occurred on 13 June has been dealt with by the school in a prompt and appropriate manner.
"The investigation of the incident has not yet been completed, but we have established that a 14-year-old boy acquired a medical lancet (8mm in length) and used it to prick around 20 others.
"The school's first action was to contact the relevant parents and provide appropriate medical advice as ascertained from the Health Protection Agency.
"The agency emphasises the extremely low health risk associated with incidents of this nature.
"The health authorities recognise that the school has followed all advice and procedures in caring and supporting our students and their families.
"It is always important for a school to maintain a calm and supportive environment and to take a proportionate view of events in order to prevent unnecessary anxiety."
Nottinghamshire Police said they had arrested a 14-year-old boy on Friday.
He was questioned and has now been released on bail, pending further inquiries, a spokesman said.