Colin Gregg, 75, from Gosforth, Newcastle, had denied nine counts of indecently assaulting four boys aged between 10 and 14.
He was found guilty by a jury at Leeds Crown Court on 3 March after a trial lasting almost a month.
Judge Robin Mairs branded him a "sophisticated, predatory paedophile" who abused his position of trust.
Gregg had "enjoyed great wealth, privilege and social standing" and used that as "a cloak of respectability", he said.
"You were a charismatic, inspiring teacher and mentor but you used those attributes to groom boys and to protect yourself from allegations," he told him.
Gregg claimed to be the victim of a "police witch hunt" and said the complainants were looking for compensation.
The assaults began in 1963 and continued over a period of almost thirty years, during which Gregg was a teacher.
He abused one child in a swimming pool and others were molested in a gym, his study or a car.
The son of the founder of the Greggs bakery chain had been head teacher at The King's School Junior School, in Tynemouth, and also taught at Durham School.
He was sent for retrial at Leeds after a jury in Newcastle failed to reach a verdict last year.
A spokesman for the children's charity the NSPCC said the case "gives hope to survivors of child abuse that they will be listened to if they speak out".
"Gregg's victims have shown incredible bravery in reliving their ordeals and it's these actions that have helped bring their attacker to justice," he said.
A statement from one of Gregg's victims, released by Northumbria Police, said: "Mr Gregg was a man who I had invested an enormous amount of trust and respect in.
"As an 11-year-old my naivety and emotional immaturity meant that the only way I could resolve this dilemma was to assume that what had happened was my own fault.
"For many years shame and embarrassment were easier to tolerate than the truth. Mr Gregg's abuse of power and trust left me with an extremely cynical and mistrustful view.
"I have never been motivated by vengeance, rather my desire has been to set reality straight and where possible to uphold the reality for others who had similar experiences.
"Looking back at this whole episode of my life, it is something that I do not wish to dwell on and I sincerely hope now that I can put it all behind me and never hear the name Colin Gregg ever again."
The heir to the Greggs bakery chain has been jailed for 13-and-a-half years for a string of sex offences against boys.