Police are investigating reports that a member of staff at a specialist education centre waved a gun at a pupil's head.
The male member of staff is said to have been joking with the pupil in a common room at the centre in Bury St Edmunds, which is not being identified for legal reasons, before making threats.
It is claimed he then left the building before returning with an antique weapon.
No shots were fired and no injuries were reported.
Suffolk County Council said police were investigating the alleged incident at the unit for children with educational and emotional difficulties on March 4.
A spokesman for Suffolk Police said: "Suffolk Police are currently investigating an alleged incident at an education establishment.
"A man has been spoken with in connection with the alleged offence.
"Officers are liaising with the education authorities to ascertain whether any offences have taken place."