The students, all aged 18, waylaid Rajesh Kannan (30) while he going home near Devakottai in the district early this morning and attacked him, police said.
He had allegedly thrashed the students after they were found drunk during the annual day of the private polytechnic last year.
The students told him that one of them lost hearing in his left ear because of the beating and stabbed the teacher's ear with a bike key.
The teacher had been admitted to a hospital.
