A teacher broke down in court today as she recalled the moment Kiyan Prince was stabbed to death outside his school gates.

Kiyan, 15, who played for Queen's Park Rangers' youth team, collapsed and died after he was stabbed in the heart outside the London Academy in Edgware, north London, on May 18.

The 16-year-old defendant, who cannot be named for legal reasons, yesterday admitted to Kiyan's manslaughter but denies murdering him.

The prosecution rejected his plea and today a murder trial started at the Old Bailey before a jury.

Liejhe Hernandez described how she witnessed "play- fighting" and thought she saw a boy being pushed against a car, snapping off the wing mirror.

She turned away and called the deputy principal on her mobile to ask for help, at which point a student called out: "Miss, miss, miss."

She turned to find Kiyan collapsed on the floor and bleeding in the arms of another student.

Ms Hernandez described Kiyan as "a lovely boy - such a really nice boy - always smiling".

Kiyan was rushed to the Royal London Hospital but the stab wound had punctured his heart and he died.

Nicholas Hilliard, prosecuting, told the jury that Kiyan had tried to break up an earlier fight between the defendant and another student.

The following day the defendant was arrested and allegedly told police it was an accident.

He said Kiyan had punched him, he then took out his pocket knife and Kiyan punched him again and then put him in a headlock.

The teen said he only wanted to leave "just a little scratch" on his arm, but it went deep "cos I never used a knife before".

"I know I got him in the stomach and the arm - that's when it stopped," he allegedly said. "I thought I stabbed him four times. I did not even know."

He had been trying to poke Kiyan in the arm - "just a little scratch there but it went deep in, cos I never used a knife before.

"I thought I stabbed him four times. I did not even know."

He was asked why he carrying a knife in the first place. "It was a little toy, it was like a toy I carried around every day."

The court was filled with Kiyan's family, including his parents, Mark Prince and Tracy Cumberbatch.

Following his death, the principal of the Green Lane school, Phil Hearne, described him as a "natural born leader" who was "an extremely reliable, hard working, bright young man".

His father said he "epitomised success in every area of life".

The attack prompted a nationwide campaign to combat Britain's knife culture and improve security in schools.