When John Rae became headmaster of Westminster School in the early Seventies the IRA was regularly setting off devices around Parliament, 200 yards from the school. Neither he nor his 479 pupils seemed unduly concerned: “A housemaster tells me that a boarder returned to his house carrying a piece of exploded car,” he wrote on March 8, 1973, “and was sent round to Scotland Yard to hand it in.” The boy wouldn’t have been gone long. With Scotland Yard also a stroll away, each school day beginning in a service at Westminster Abbey, and Rae a guest at 10 Downing Street and the US embassy, there is throughout these diaries of his 16-year reign a vivid sense of proximity to the heart of British establishment life.

 It’s a mark of his gifts as an observer of human behaviour, an analyst of power politics, and an urbane prose stylist that the memoir merits the attention of any reader. Although it may be set in a rarefied world, its central theme is universal – the transition from childhood to adulthood. Rae’s overwhelming interest is his pupils (despite the book’s rather crass and misleading title) who he finds absorbing: “Westminster’s boys and girls were no angels,” as he puts it, “but they were always good company.”

As we follow his campaign to turn a single-sex establishment with a reputation for arrogance, slackness and drug-taking into the best school in the country, the same holds true of the author.

Rae died in 2006, aged 75, but the energy he displays here is prodigious. He teaches history to pupils of all ages, navigates tricky meetings with staff and governors, soothes a truly bizarre array of parents, courts new teaching talent and new sources of bright students, chairs the Headmasters’ Conference, passes judgment on thieves and pyromaniacs, pounds the pool at the RAC club, raises six children.

All the while he has an appetite for controversy and debate, writing books, a column in the Times Educational Supplement and frequent articles for the nationals. Even as the cyclical patterns of academic life repeat themselves, his writing remains fresh, droll and often poignant.

Some incidents are shocking. A housemaster asks to see him about a 16-year-old who is increasingly disaffected. They discuss the child’s home life. His father committed suicide when he was six, it emerges. He asked the boy to come into his room, took out a revolver and shot himself in front of him.

Some are farcical: a colleague drops dead en route to his own farewell party; Rae leads the decision among the hungry guests not to waste a perfectly good dinner. He then finds himself sitting next to the historian A J P Taylor, whose son was at the school. “You can always tell a Westminster,” says Taylor, “because his handwriting is illegible and he can’t walk properly.”

In key areas Rae is shown to be ahead of his time. Long before most headmasters had understood the value – indeed necessity – of nurturing a profile, Rae was courting the media. It made him enemies inside the school and in the wider world of education, but how astute and prescient he seems now.

To the accompaniment of howling and lamentation from his fellow headmasters, he allowed the first ever reality television broadcast about a public school to be shot at Westminster, inviting BBC cameras in to make a fly-on-the-wall documentary in 1979. The film that emerges is, he feels, a true one, catching “the lively, articulate flavour of the place, as well as the worries about success and failure, and about parental sacrifice”. The press are almost universally enthusiastic about both the film and the school. Rae is quietly jubilant.

As a surreal cast of characters float past (Thatcher, Wilson, Tommy Trinder) he oversees the arrival of girls in the sixth form. He places as much emphasis on pastoral care as on academic excellence, and has long since abolished corporal punishment.

He goads his fellow headmasters about their lack of transparency, insisting that it is in the interest of all schools to publish their exam results. It helps, of course, that his are so good.

Others mutter about his ‘‘Gadarene pursuit of A-level results’’, but towards the end of his time in charge he places 79 pupils from a single year at Oxbridge colleges. Whether Oxbridge matters a damn is a moot point, but in Rae’s world admissions are, and indeed remain, the measure by which many schools judge themselves.

When he finally leaves Westminster, there are 566 boys and 78 girls in the school. To them, as well as many of his staff, Rae sees himself as a father figure, and it is moving when he writes about the death of his own father, a radiologist. He stood for simplicity, reliability and loyalty to the family: “His outlook on life was balanced, humane and unsentimental.”

He did not espouse that sense of entitlement that so often blights public school education, but instead a sense of possibility.

If this exceptional man betrays one fault it is that air of assumed omniscience to which all headmasters ( and indeed some priests!)are prone.