Patrick Marshall, 70, of Churt, near Farnham, was found guilty of 24 counts of indecent assault against nine boys and teenagers and one count of indecency with a child.
The assaults took place between 1969 and 1981, Southwark Crown Court heard.
At the time, Marshall taught at what was Windsor Grammar School, Berkshire, before moving to St Paul's, Barnes.
The court heard the assaults took place in the defendant's car, the victims' homes and abroad.
During the trial, one witness said he "lay there quietly" while he was assaulted by the geography teacher and rowing coach at a "secluded" building used by the school.
"I just felt intense discomfort. I did not know how to stop it from happening," he said.
Marshall was convicted by a jury of seven men and five women who returned a unanimous verdict on all counts at the end of a six-week trial.
The father of three shook his head as the verdicts were read out.
A former teacher has been jailed for 17 years for sex offences committed against boys over more than a decade.