Phillip Nix, 50, who worked at a number of schools in Lincolnshire, was also ordered to register as a sex offender for life and disqualified from working with children for life.
Nix, of Hainton, near Louth, denied seven charges of indecent assault on a male, two charges of indecency with a child, two charges of sexual activity with a child and three other serious sexual offences.
A jury at Lincoln Crown Court heard 13 of the charges related to one boy who Nix began “grooming” when he was just ten years old.
Nix chose not to give evidence from the witness box but was convicted of all 14 charges at the end of a two-week trial.
The jury returned unanimous verdicts on all 14 counts after deliberating for two days.
The offences occurred between April 1999 and December 2004. Both of Nix’s victims cannot be identified for legal reasons.
Passing sentence, Judge Sean Morris told Nix: “You have been a teacher for many years at some of the most prestigious state schools in the county.
“You have let them down.”
Judge Morris told Nix it was also clear he had “groomed” one of his victims.
“Your downfall was that this boy grew up to be a bright, intelligent, talented young man who struggled with this dark secret until it became so heavy it came out,” Judge Morris said.
Nix was also made the subject of a sexual offences prevention order which will remain in place on his release from prison.