A 15-year-old boy who stabbed a student at Ashwood College remains in custody as the juvenile justice authority has opposed his release on bail.
The boy was on parole on February 1 when the incident occurred.
Youth Justice was concerned about his release and his lawyer did not request bail.
Police told the children's court that the victim was afraid of further attacks and had received threatening messages on Facebook from friends of his assailant.
The children's court was told that the accused, who cannot be named, thought his victim had "dobbed in" some mates for committing a burglary.
The boy, who was expelled from the school last year, stabbed his 15-year-old victim on the inside of the right forearm with a knife similar to a box cutter, causing serious injuries that required surgery.
The accused pleaded guilty to charges of intentionally causing serious injury and possessing a controlled weapon. Two other charges were withdrawn.
A police detective said the boy was on parole for a similar stabbing assault on a victim he believed was worthy of "retribution".
He had also previously been found guilty of trafficking and theft, and charged via summons over an incident in January last year. The charges were intentionally causing serious injury, recklessly causing serious injury and assaulting a person by kicking.
The victim's recovery will not be known for weeks. The mothers of the victim and the accused were in court.
The accused will face court again on February 25. A pre-sentence report will be prepared by Youth Justice.
— with Daniel Tran