In a courtroom packed with supporters, Canadian administrator Neil Bantleman - who also holds British nationality - and Indonesian teaching assistant Ferdinand Tjiong were found guilty of abusing three young boys at the Jakarta Intercultural School.
Both men have strongly denied committing abuse, and received backing from pupils' parents and the school, which has for decades been favoured by expatriates and wealthy Indonesians in the capital.
Following the verdict, Canada called for due process to be followed, Britain noted irregularities in the case, while America said it was "deeply disappointed" and warned the outcome could damage Indonesia's reputation abroad.
After an all-day session reading the verdict at South Jakarta District Court, presiding judge Nur Aslam declared both men guilty of abusing the children.
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Passing judgement on Bantleman, she said: "The defendant did not admit his crime or express regret for his deeds, nor did he apologise for what he did, which psychologically damaged underage children."
To applause and cheers from his supporters, who included many parents at the school, Bantleman said that he would appeal the verdict: "We will continue to fight until the truth comes out."
Her voice breaking with emotion, his wife Tracy said that she was "deeply disturbed and appalled by the decision of the panel of judges".
Tjiong also said he would appeal the verdict.
The scandal at the school - formerly known as the Jakarta International School - began in April last year with accusations that cleaning staff abused a nursery school boy, and was quickly followed by claims of abuse from other parents.