Zadie Smith is the most talked-about first novelist of the spring. Her debut novel lives up to all its publishers’ promises and does one thing it didn’t promise to do: it gives a simultaneously funny and moving account of how children of all cultures become who they are, and where adult intervention can go wrong.

The sprawling narrative opens on New Year’s Day 1975 and closes on New Year’s Eve 1992, backtracking to the Indian Mutiny and the 1907 Jamaican earthquake to explore the “root canals” of the past as it affects two north-west London families, the Iqbals and the Joneses, and especially their teenage children.

Samad Iqbal, a Bangladeshi Muslim, sees out the Second World War in the same tank as Archie Jones, a white working-class Londoner, and they bond during a bloody episode in Bulgaria. Theirs is “the kind of friendship an Englishman makes on holiday ... that crosses class and colour, that takes as its basis physical proximity and survives because the Englishman assumes the physical proximity will not continue”. In fact, the Iqbals and the Joneses are destined to live in each other’s pockets for the final quarter of the 20th century, most of the time to their mutual benefit.

The main chapter in their joint story begins when Archie, now middle-aged, is saved from suicide by a halal butcher on Cricklewood Broadway on New Year’s Day. Later the same day, he meets his second wife Clara, a much younger black woman who rebelled against her Jehovah’s Witness mother. Meanwhile, Samad and his wife Alsana have emigrated to Britain and settled nearby. Their twin sons, Millat and Magid, and Archie and Clara’s daughter, Irie, grow up together.

Most of what follows centres on how the young adults choose what to keep and what to discard from their cultural baggage. A captivating plot delivered at speed, acute characterisation, writing that captures the clamour and edginess of London’s multicultural fringes and an acid wit make it a very readable tale.

The author has said that she thrived on her own schooling (at Hampstead School, a comprehensive, followed by Cambridge). “Glenard Oak School” (a name of long-buried significance in Irie’s family), which Irie and Millat attend, is obviously a work of fiction. There is an affectionate spirit in the portrayal of its pupil clans, no-go areas and a head who has been on too many courses in conflict resolution and appears powerless to stop pupils drug-dealing, let alone smoking.

Zadie Smith is too young to have taught in an inner-city school through the 1980s, but she must have known a few flies on the wall. One sharp scene is set at a parents’ meeting at the Iqbal twins’ primary school, where the voluble Samad lobbies for the abolition of the “pagan” Hrvest Festival - just before he starts an affair with the painfully PC music teacher.

Samad, a particularly touching figure, is a clever man doomed to serve curries and pints to the ignorant, and to be disappointed in his sons. Millat’s thirst for clan warfare (assimilated more from Al Pacino and Marlon Brando than from his own history) leads him to join a fundamentalist Islamic organisation with the sorry acronym KEVIN.

The studious Magid is sent back to Bangladesh for his education (after the ever-loyal Archie has helped Samad to kidnap him, heralding a bleak chapter in the Iqbal marriage) and, to his father’s distress, picks up colonialist sympathies.

Of the three friends, Irie is the most troubled by her identity and, arguably, the child most drastically failed by her teachers and others who miss the opportunity to make a difference. She is smitten with the hearthrob Millat and vows to straighten her hair after a discussion with a white English teacher about Shakespeare’s Dark Lady. In a poignant scene involving a hairdresser’s botched job, she buys an Asian girl’s freshly shorn locks in a dodgy Dickensian haircare emporium.

The beauty parlour mishap is pivotal for Irie: soon afterwards she and Millat drift into the orbit of the upper-middle-class-bohemian Chalfen family as a result of the well-meaning head’s study support scheme.

Smith has reserved her cruellest barbs for the construction of Joyce Chalfen, a feminist horticulturalist bursting with “the Responsibility of the Intellectual”, who sees her son’s classmates as case studies in the importance of nurture - all good material for her appearances on Gardener’s Question Time. There are wickedly toe-curling exchanges round the Chalfen table of the “and where do you come from originally?” variety.

Irie falls painfully in love again, this time with the Chalfens and their lifestyle, but their interest in her proves to be superficial.

The monstrous Joyce’s husband Marcus, a scientist, becomes an unsuitable mentor for the obsessive Magid. As Marcus’s long-term project to clone a “FutureMouse” reaches fruition, it fuels another crucial sub-plot with a clever twist that you see coming, but only just.

The metaphor of the deep-rooted teeth as the only obviously white part of the non-white characters needs some disentangling: Irie hates her teeth more than her hair and leaves home when she is bitten by her mother’s false ones. Magid brushes his six times a day as an expressionof his intellectual rigourand the elderly racistex-soldier whom the three friends visit as children hasno teeth at all.

There’s probably a future PhD to be written on teeth in the work of Zadie Smith, but that’s someone else’s problem; I’m just going to enjoy her next novel.

Geraldine Brennan