Some 50 disabled, particularly hearing and speech impaired and mentally challenged persons were staying at the Neyam school in Kuttayur.
The 20-year old girl reportedly told some persons, supplying vegetables and provisions to the school, in sign language that she was sexually assaulted by the 57-year-old instructor, Vanangamudi, a week ago, police said.
Following a complaint lodged by an NGO, which was apprised of the incident, police took Vanangamudi into custody for interrogation, police said.