The accused was arrested yesterday on the complaint of the girl's mother, they said.
The incident came to the fore on Friday after the child tried to narrate her ordeal to her mother. Unable to understand what she was trying to say, her mother took her to the institute on Saturday, they added.
A woman therapist at the institute explained to the girl's mother what her daughter was trying to convey to her.
After realising that her daughter had been sexually assaulted, the girl's mother approached the police and a case was registered, a police official said.
The accused had been working at the institute for the last five years, they said, adding the police is probing whether he had sexually assaulted other students of the institute or there were any complaints of a similar nature against him.
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