A teenager admitted at the Old Bailey to killing 15-year-old Kiyan Prince outside the boy's school gates.
The 16-year-old, from north London, who cannot be named because of his age, has denied murder but admitted manslaughter.
His trial on the murder charge is due to open on Tuesday.
Kiyan, a promising footballer who played for Queen's Park Rangers' youth team, was stabbed to death near the London Academy, Edgware, on May 18 this year.
The stab wound to Kiyan's chest pierced his heart.
His killer, wearing a grey suit with an open-necked white shirt, stood behind his legal team to plead guilty to manslaughter when that alternative charge was read to him.
But because the prosecution does not accept his plea to the lesser charge, his trial for murder will take place before a jury.
