The boy had died on October 11 after the school headmaster M Ayyanna in Kavali town of the district allegedly slapped him and he accidentally fell on a kitchen slab at the residential premises of the school. The boy later succumbed to injuries he received on his nape, they said.
"During the course of investigation, it came to light that the headmaster reportedly had an affair with the lady teacher and the boy had seen them in a compromising position," DSP (Kavali) D Mohan Rao said.
During the probe, police found the role of the headmaster behind the death of the boy and registered a case in connection with the incident under sections 304 (culpable homicide not amounting to murder) and 201 (causing disappearance of evidence of offence, or giving false information to screen offender) of IPC.
The headmaster and the lady teacher Kausalya were subsequently arrested last evening, the senior police officer said.