An online video showing schoolboys fighting in Co Armagh has been viewed almost 1.5m times.
The clip was shared on a number of social media sites, including Facebook. Lasting less than a minute, the footage shows a group of schoolboys from St Patrick's Grammar School standing in a car park in Armagh.
Two students engage in a fight before other teenagers become involved in the fracas.
The brawl continues until an adult intervenes.
Principal Dominic Clarke said the incident took place eight months ago and had since been dealt with.
He added that the emergence of the clip highlighted the dangers of this type of content appearing online.
"It is now there to be regurgitated again and again," he told the Ulster Gazette.
"Unfortunately we don't have any control of who takes these clips and what they do with them. It happened last year and it was dealt with effectively by my predecessor and those involved. We have real concerns that the material has resurfaced.
"I would appeal to anyone who has had the video shared with them not to pass it on.
"The clip appearing online has caused great anxiety. I hope that the significant work undertaken with the students involved has not been undone by this."
He also urged young people to give careful consideration to what they choose to upload and post on social media.
His comments came as the PSNI was called to a Co Tyrone school following a clash between two students yesterday.
Staff at Holy Cross College in Strabane were forced to call police after attempts to break up the fracas failed and more pupils joined in.
One male student was arrested, but was later released into the care of his parents.
A mother of a pupil at the school said her child was too afraid to go back.
The Strabane woman, who did not wish to give her name, said that her young daughter was caught up in violent disturbances.
"She told me there were chairs and plates being thrown and tables tumbled," she added.
"My little girl said that it was just a free-for-all, like a brawl.
"She said there were people punching each other viciously and that there was blood and food all over the ground.
"She told me that a teacher was stooped down trying to help a young man on the ground and a pupil lifted a chair and hit it off his back at full force."
Maria Doherty, the school's principal, said 600 students were in the canteen at the time of the incident.
"We decided to call the PSNI because of the number of students we had in the canteen and social area at that time and the potential this situation had to escalate, so it was a supportive role," she explained.
The PSNI said there were no serious injuries.