A former teacher convicted of sexually assaulting boys at one of Canada's most prestigious private schools has been sentenced to three years in jail.

Doug Brown, 55, was found guilty in October on nine charges of indecent assault involving students at Toronto's Upper Canada College.

"He stole from them that which can never be returned, their innocence," Superior Court Justice Harry Laforme told the court. "There must be a serious price paid for such theft."

Brown must also submit a DNA sample and will be listed on the national sex offender registry.

Defence lawyers wanted the judge to impose community supervision with conditions, while the Crown wanted Brown to serve four to six years in prison.

The former teacher pleaded not guilty to 12 charges of sexually abusing boys during late-night visits to the school dormitory in the 1970s.

Seven students aged 11 to 13 at the time of the incidents testified the former English teacher touched them inappropriately. Some testified that the abuse led to depression and other problems later in life.

Brown was let go from the school in 1993 after accusations about inappropriate behaviour.

At his trial, Brown said he received a year of severance and a letter of reference from the school and he said he was told not to talk about the scandal.

An Ontario court previously approved a settlement reached in 2003 between the school and former students who said Brown sexually touched them.

Brown faces a second criminal trial on charges he molested another student.