He would not immediately say how the department learnt of the alleged abuse.
Police said the teacher had exposed his pupils to porn before sexually assaulting them.
His alleged victims, seven boys and a girl, were allegedly all grade seven pupils, said Brig Leonard Hlathi.
“It is reported that the teacher had been violating the learners from March 2019 until he was exposed in September.
“He would allegedly call them over to his desk during class, show them pornographic videos as well as images and lure them individually to a storeroom to commit his evil deeds,” said Hlathi.
The teacher was arrested on Wednesday after a month-long investigation by police. He appeared in the Tonga Magistrate’s Court on Thursday where he was granted bail. His case has been postponed to January 2020.