The boy, 15, pleaded guilty to 'Robbery armed with an offensive weapon' and was sentenced at Queanbeyan Local Court on Monday following the attack of Tuesday, July 2 last year.

The court heard that the accused and two of his friends witnessed a fellow student walk into the Karabar shopping centre at around 12pm that day. The accused then followed the victim out of the shops and accosted him near Margaret Donoghue Oval, where he grabbed him and asked "what have you got in your pockets?" while brandishing a kitchen knife.

The victim turned over $6.50 in cash and a mobile phone before he was let go. Police arrested the accused later that day after the attack was reported.

His solicitor told the court that the accused was no longer associated with his former friendship group, and had since left the school to take up distance education. He would also undergo work experience in a trade with his father, the solicitor said.

"He's burned his bridges with that particular group of people.

"For a young man as impressionable as my client ... he has the opportunity to have a more positive circle of people around him, and he has the opportunity to gain some work experience."

While Magistrate Chris Bone took into account the youth of the accused in sentencing, he said it was a "very serious" offence.

"I think the teenage years are the hardest part of life.

"You're halfway between being a child and an adult ... and it's very, very difficult.

"But I'll say this: every kid knows it's wrong to pull a knife on another kid. You just know that instinctively," he said.

Magistrate Bone sentenced the accused to a two-year good behaviour bond to be supervised by Juvenile Justice officers.