The 14-year-old boy, who cannot be named for legal reasons, described how Mr Lawrence, a father of four, jogged up to a Triad gang member - who was wearing a hood, black hat and scarf across his face - and tried to reason with him outside the front gates of St George's RC school in Maida Vale, north-west London.
"Mr Lawrence said to the Triad `We can sort something out about this'," the witness said.
Demonstrating with a round-arm motion, he described how the gang member stabbed the headmaster in the chest after punching him in the face. "The Triad dropped a knife from his sleeve and he stabbed Mr Lawrence in the chest," he said.
He said he had had a clear view and the blade had been seven inches in length.
"The Triad jogged up the hill. Mr Lawrence went back toward the school. He passed me. He was holding his shirt. He was staggering and holding his side."
The prosecution alleges that Mr Lawrence was killed after a running feud between two teenage boys at Mr Lawrence's school had led to the armed gang ambushing one of his pupils in a revenge attack.
One of the gang, who had played truant and "tagged along" because he heard it might be "a laugh", later described Mr Lawrence's murder as "disgraceful". The 16-year-old boy, who also gave evidence yesterday, said he was originally arrested in connection with the killing.
On the way to the police station he told officers that another teenager had admitted stabbing the headmaster. "What was important to me was telling the truth and I told the truth," said the boy.
He agreed he had said to police that the other teenager's action had been disgraceful. Asked by the defence counsel, David Spens QC, whether that had always been his attitude, the boy replied: "Yes."
He said he had tried to cover up his truancy afterwards by getting himself marked on the school register for that day. He agreed he did not want it to be known he was at the murder scene.
But another reason was that he was in trouble with the school over truancy. "One more offence and they would have expelled me," he told the court.
"I did not think I would get arrested because I did not do anything."
A teenaged boy charged with Mr Lawrence's murder, who cannot be named for legal reasons, denies that charge and two further charges of conspiracy to cause grievous bodily harm and wounding with intent.
A co-defendant, aged 15, also denies the latter two charges.Reuse content