Former teacher Charles Napier has been sentenced to 13 years in prison for sexually abusing 23 boys between 1967 and 1983.
He admitted 30 indecent assault charges and one offence of indecency towards a child. All his victims were under 16.
Many of the counts included multiple incidents and are estimated to account for hundreds of individual assaults.
Napier, from Sherborne in Dorset, was at one time treasurer of the Paedophile Information Exchange.
The group campaigned on behalf of paedophiles in the 1970s and 1980s.
The judge said there was "no doubt" he had become a teacher because of the proximity it offered him to young boys, some of whom had been "dramatically damaged" by his crimes.
The court heard that one boy was indecently assaulted on eight separate occasions between 1969 and 1972.
Napier forced another boy to commit a sex act on him.
Francis Wheen, a victim of Napier who has waived his right to anonymity, told the BBC how the teacher would win boys' trust by offering them sweets, fizzy drinks and cigarettes.
He related that he stayed away from Napier after the teacher tried to put his hand down his shorts, but others had suffered more serious abuse which left them "very badly damaged".
"He was in a position of trust which he abused wholesale," said Mr Wheen.
He was cleared of one other charge in October because of lack of evidence.
Much of the abuse took place in a workshop at the school where he taught.
Napier is the half-brother of Conservative MP John Whittingdale.
He left the school in the early 1970s and went on to hold jobs working with children in Cairo and Sweden.
'Arrogant and controlling'
Prosecuting, Peter Clement said Napier "exploited his role and his position of trust for his own sexual gratification".
Acting Detective Chief Inspector Keith Braithwaite described Napier as "an arrogant, controlling and manipulative individual who has shown no remorse".
Det Chief Insp Braithwaite thanked those who came forward to give evidence, adding that he hoped the sentence indicated how seriously the courts take such offences.
He was arrested in 2013 as part of Operation Cayacos, one strand of Scotland Yard's wider investigation into historical child abuse called Operation Fairbank.
Operation Fairbank was launched in 2012 after Labour MP Tom Watson wrote to the police about allegations of a paedophile ring linked to Westminster.
During interviews with the police Napier told officers he had been "completely out of control" and was "desperately sorry" for his actions.