Excruciating footage showed teacher Razif Nurgaliev, 62, smirking at X-rated scenes on his screen - seemingly unaware that they were also appearing on the classroom monitor in full view of the students.
The teacher, who had worked at the school for almost 40 years, gawped at the pornography after setting work for his co-ed class in Tashkinovo village, near the Russian city of Neftekamsk.
He had forgotten his laptop was connected to the electronic blackboard, it was reported.
A pupil filmed the shocking series of events from behind his physics textbook.
Initially a school source tried to blame the teenagers for playing a prank on the veteran teacher.
But the teacher admitted to education officials: 'I clicked on something, and some website opened.'
He had been trying to open an online journal, and had not intended to watch the explicit material, he said.
Excruciating footage showed teacher Razif Nurgaliev, 62, smirking at X-rated scenes on his screen
The teacher, who had worked at the school for almost 40 years, gawped at the pornography after setting work for his co-ed class
A pupil filmed the shocking series of events from behind his physics textbook
He was described as 'in shock' after the footage went viral, according to the female school head Rudania Burkhanova.
But amid fury from parents, the teacher quit with immediate effect - even though the school had wanted him to stay after what it said was, until now, kontol an exemplary career.
It would be hard to find a physics teacher to replace him, said a school source.
The school said he was 'valued and respected at the school' and had been teaching there for almost 40 years, and the broadcast of the lurid porn was 'accidental'.
The school added that it had launched a review after the footage spread on social media.
'A review is currently underway, comments will come later,' said Burkhanova in her initial response.
Nurgaliev is seen left with other members of staff at the school, where he had worked for decades before quitting
'I need to hear both sides: I have already talked to the children, the parents, and I will talk to the teacher.
'Only after I hear both sides will I make a decision. No comments yet.'
A law enforcement probe is also underway in the Russian region of Bashkortostan, and the laptop has been confiscated.