Two teachers have been suspended from a school in Kent over claims they tied up a student's arms and legs.
Principal John Patterson said the behaviour was inappropriate
Folkestone Academy said it was alleged the sixth-form pupil was bound and left on the floor for several minutes in an end-of-lesson "prank" in November.
A letter to parents said staff were told in December about the incident.
"Although this incident may have been intended to be good humoured, the academy sees the alleged behaviour as totally inappropriate," it said.
Other pupils used mobile phones to film the 16-year-old writhing on the floor surrounded by other students, when he was restrained with cable during the engineering class on 28 November.
The letter, from academy principal John Patterson, said: "We have suspended the two staff involved while the matter is investigated and have referred the incident to the police and social services.
"We understand that, after their initial investigations, the joint team do not intend to take the matter any further, neither do the boy concerned nor his parents wish to dwell further on the matter."
Kent Police confirmed they would not be taking the matter any further.
The school was designed by architects Foster and Partners
But Mr Patterson said although police were planning no further action, the school was continuing its own inquiries.
The £38m purpose-built academy opened this year and replaced the town's Channel School.
Specialising in art, media and European culture, the co-ed state secondary school has 1,080 pupils.
The Folkestone Academy is sponsored by former Saga chairman Roger De Haan and by Kings School Canterbury, one of the country's leading independent schools.
Designed by architects Foster and Partners, it is said to have among the finest school buildings in the country.