The victim, 17, was left blind in one eye after he was hunted down by three youths at Riverside College, Widnes, in December following a "trivial" scuffle.
Michael Jones, 18, of Widnes, pleaded guilty to causing grievous bodily harm with intent and pleaded guilty to possession of an offensive weapon.
He has been detained for nine years.
Seventeen-year-old Jamie Grimes, who had "bad blood" with the victim, admitted causing grievous bodily harm with intent and was detained for five years for his part in the attack.
He denied knowing that Jones had the scissors, which was accepted by the prosecution.
Lewis Connor, 18, of Lune Way, Widnes, who was also with the pair, was given a 12-month community order after admitting putting a person in fear of violence.
Judge Neil Flewitt QC told the trio there was "no justification or excuse" for the "appalling" attack.
Liverpool Crown Court heard the victim, who has undergone four operations, may yet lose the eye itself and feels his "whole life has been destroyed".
The court heard the trio went from classroom to classroom hunting for their target following an altercation between him and Grimes.
When they found him in his maths class, the door was locked but the teacher Ken Wong heard a loud bang and the defendants burst in.
Grimes, of Steward's Avenue, Widnes, threw "forceful punches" on the boy before Jones, of Caldwell Road, stabbed him in the eye, chest and hand with decorating scissors in front of horrified pupils.
All three boys then fled.
Judge Flewitt, QC said Jones "has a propensity for violence... and for carrying serious weapons".
"You are clearly and will continue to be for some time a dangerous young man," he said.
On sentencing Grimes, the judge said it was "your fight... and you whipped up that group to look for the victim".
"You set loose the mayhem that followed," he added.
In an impact statement, the victim said he had given up his college course, lost his friends and was conscious of his appearance and feared that he would never work again.
Insp Chris Adkins, of Cheshire Police said it was a "pre-meditated, extremely violent attack, leaving the victim with horrific life-changing injuries".
A "dangerous" teenager who blinded a student by repeatedly stabbing him with scissors in front of his teacher and classmates has been detained.