Nigel Pipe, aged 87, was locked up following a three-week trial at Nottingham Crown Court, in October last year.
A jury found Pipe guilty of 27 offences, including four counts of buggery, nine counts of indecency with a child and 14 counts of indecent assault on a male, while working at Skegby Hall.
The Ministry of Justice confirmed that Pipe, formerly of Llanwenarth View in Govilon, Abergavenny, died in hospital, on January 5.
The Prisons and Probation Ombudsman, who routinely investigates all deaths in custody, has been informed.
An inquest to determine the cause of death is scheduled for February 2, at Nottingham Coroners’ Court.
Passing sentence, Judge Julie Warburton told Pipe: "You are someone who sought out and preyed on young and vulnerable students, quietly controlling them with your calm manner.
"You were in a position of trust and in the course of this position you abused that trust in the most heinous of ways."
Speaking after the trial, Detective Constable Neil Beddoe said: "Until you have met and interviewed victims of childhood sexual abuse, it is difficult to understand just how damaging these acts can be.
"These men have all had to live with the burden of what happened to them as children and have, in many cases, experienced considerable challenges in their adult lives as a result."
The school was closed in 1992.