Presiding judge Mohamad Yunus told the South Jakarta district court that Afrischa Setyani, the only female cleaner among five defendants, "was found guilty of assisting in violence and sexual abuse of children".
"We sentenced her to seven years in prison and a fine of USD 8,000," he said.
Her sentence was lower than the prosecutors' recommended 10 years.
The judges were also expected to deliver verdicts today on four male cleaners -- Agun Iskandar, Virgiawan Amin, Zainal Abidin, and Syahrial, who goes by one name.
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Several of the cleaners who originally confessed have since recanted, claiming they were beaten by police.
The family of the abused boy is suing the school and seeking USD 125 million in damages.
Setyani wept after the verdict was handed down but refused to speak to reporters.
Her lawyer Isdarwati Aprihadi maintained her client never confessed and said she would appeal.
Canadian Neil Bantleman, an administrator at the school, and Indonesian teaching assistant Ferdinand Tjiong, are also on trial separately, accused of sexually assaulting children. They deny the charge.