William Bain, also known as Bill, was due to stand trial at the High Court in Glasgow on 30 June 2025 but instead pleaded guilty to 11 charges.
The 72-year-old admitted sexually abusing 11 children between 1978 and 1999 while working at three independent schools across Scotland.
He subjected two boys to lewd, libidinous and indecent practices at the capital's Edinburgh Academy, where he also held the role of house tutor.
Bain targeted a third child while working at Robert Gordon College in Aberdeen, where he was also employed as a house master
He then began working at Keil School in Dumbarton and went on to sexually abuse a further eight pupils.
Following his admission of guilt, Bain was jailed for nine years in prison with his name added to the sex offenders register for an indefinite period.
Fiona Kirkby, Procurator Fiscal for High Court Sexual Offences, said:
"William Bain is a prolific offender who repeatedly exploited his position of trust as a teacher to sexually abuse children in his care.
"He has now been held accountable and imprisoned for his depraved actions.
"This prosecution should send a clear message to those who sexually abuse children and young people, regardless of how much time has passed.
"I would urge anyone affected by similar crimes to report it when they feel ready and able to do so.
"You will be listened to and supported as we use all the tools available to us in seeking justice."