The Bolsover School confirmed a member of staff had alerted police to an assault by ‘someone outside of the school community’ on May 17.
Derbyshire Constabulary said the incident was reported just after 3.10pm.
A teenager attended hospital due to concerns they may be injured.
“We do not believe they were required to stay in hospital,” Derbyshire police said.
“Enquiries are being carried out and officers liaising with staff at the school in relation to the incident.”