But the attack at the tough comprehensive, since closed down because of its problems, did not deter him from the hard world of inner-city teaching. Mr Lawrence came from a privileged background - he was educated at Ampleforth, Britain's leading Roman Catholic public school. - but it was to underprivileged children that he came to devote his career.
The aspects of teaching that public-school masters can more or less forget about - reading, writing, numeracy, discipline, security of the buildings - were his everyday concerns, and those who knew him say that when he addressed them, he did so with conspicuous success. At St George's, Maida Vale, the Roman Catholic comprehensive where he met his death on Friday, he inherited serious disciplinary and academic problems. It was a school, said Cardinal Basil Hume yesterday, "which needed turning round".
Mr Lawrence turned it. He did so by initiatives as varied as padlocking gates and retraining specialist-subject teachers to teach basics such as reading. "We inherit an acute literacy problem when the children come at 11-plus,'' he said in an interview last year. "We are having to retrain mainstream teachers, of history, for example, to teach children to write at the same time. There is no point trying to teach complex aspects of the curriculum to pupils who have not even mastered the basics.''
He bought new padlocks to put on doors and gates, and kept a check on all visitors. "Parents expect that when they send their children to school they will be safe and secure, and the children learn best when they do feel safe and secure," he said.
Under the firm disciplinary regime he established, exam results shot up, and parents began competing to send their children to St George's, which has been very much an inner-city success story, with more than 200 pupils added to the roll under Mr Lawrence's tutelage.
His teaching career began in 1969 in more privileged surroundings, as an English master at St Benedict's school in Ealing, west London, run, like Ampleforth, by Benedictine monks.
He steadily progressed, however, to the state sector, through Gunnersbury school in Brentford, St Mark's School in Hounslow and then on to Dick Sheppard.
"Although he came from quite a privileged background, he always wanted to teach in the state sector and help children with few advantages," said Dennis Costello, who taught with Mr Lawrence at St Benedict's.
"He was the kind of person who would confront difficulties. He was not prepared to hide from them, and, sadly, that led to his death," said George Varnava, president of the National Association of Head Teachers, who worked alongside Mr Lawrence when both were south London heads.
"The problem with inner-city schools is that you spend so much time dealing with disciplining children that you can get diverted from teaching. Mr Lawrence tried to tackle both.
"At Dick Sheppard he was dealing with kids who had a high level of deprivation and were used to violence as part of their lifestyle. He was a tough man and there were aspects of him that derived from his own education, yet he was also quite visionary."
Winston Castello, the chairman of the Dick Sheppard board of governors, said: "He was not a Rambo character in any way, but I think he would have been very protective towards his pupils. He was not confrontational and he would always try to reason with people."
n Violence in schools has been rising in the Nineties, Nick Cohen writes. There have been no national figures since 1989, when Lord Elton carried out an inquiry and told the Government that two per cent of the country's 400,000 teachers had reported facing physical aggression. But it is known that expulsion of children from schools - in most cases for violent or disruptive behaviour - has rocketed. In 1990, 2,900 children were excluded; this year 14,000 are expected to be told to leave.