“An excellent hagwon,” according to one of the characters in Min Jin Lee’s new novel, “is everything.” Every year, Korean parents pay hefty sums to send their children to these private after-school academies designed to turbocharge academic performance, where they spend evenings and weekends being drilled in mathematics, reasoning and essay technique. In the third book in what she has called her Diaspora Quartet – a follow-up to 2017’s Pachinko, recently named one of the New York Times’s top 100 books of the 21st century – she presents the fierce competition to snag a spot at those hagwons deemed the best as symptomatic of Korea’s scarcity mindset: in a country where university places and white-collar jobs are hard to come by, everyone’s looking for an edge. But over the course of the novel’s 650 pages, they also come to stand as symbols of pretty much everything you can think of: of country and culture; of failure and success; of responsibility, or the lack of it; of what it means to achieve, and of what, in the final analysis, the purpose of our achievements might be.

The action in American Hagwon unspools over nearly three decades, and crisscrosses from Seoul to Sydney to California and back to Seoul again. At its centre is the Koh family: John, Helen and their three children, Bo, DH and Mido. When the novel opens in 1992, their life in Korea appears comfortably middle-class – John is a senior manager at a multinational corporation; Helen is an upmarket saleswoman, her commissions covering the children’s hagwon fees. But they are dramatically capsized: first by a personal betrayal and then again, in a brutal one-two, by the financial crisis that clobbered Asia in the late 90s. The family move, then later move once more: sometimes together, more often following their own trajectories; but always connected, and supporting one another as opportunity and need ebb and flow between them.

At every point, John and Helen put their children’s futures above their present comfort: education – seen as the surest route to security and self-worth – is prioritised above all else. In California, John fries fish and sluices the floors of the grandly named Shrimp Castle; Helen sells “imported face cream and handbags in a makeshift Korean department store that looked like a warehouse”. Every spare penny goes towards the astronomical expense of the trio’s academic careers: the essential which cannot be ducked.

This is the novel as luxurious full-body experience: it feels like stepping into a longstanding family gathering

This is, then, a family affair – but it soon becomes clear that, for Lee, the definition of family is elastic. The novel’s canvas is global, but the intertwined, intricate expat community it presents has the feel of a village. Friends, relatives and rivals move in close orbit, defined and bound together by their shared roots, their roles evolving as the years pass: sometimes bolstering one another with jobs and advice and connections, sometimes renewing decades-old feuds.

The novel’s expansiveness means that the people on the page come to appear as living, breathing beings – complex, contradictory, known intimately to each other but often unknowable themselves – to the point where being in their company feels like stepping into a longstanding family gathering. This is the novel as luxurious full-body experience: both in its patient tracking of the highs and lows of its characters’ lives, and in the compassionate realism with which it observes them, it reminded me of nothing so much as George Eliot’s Middlemarch – and, as with Eliot’s masterpiece, the effect of reading it is both immersive and transformative.

Related: ‘I thought, if I’m going to die, I’m going to write a book first’: Pachinko author Min Jin Lee

But it’s also, like Pachinko before it, a treatise on the Korean diaspora, and specifically on the role of the hagwon within it. When youngest child Mido finds work in the portentously named Fortress, a hagwon catering to the children of their southern California expat community, the novel tilts on its axis. Suddenly, we’re seeing the hagwon from the other side: not as supplicants at the fortress’s gate, but rather as its gatekeepers; guardians of the bright future it promises. Fortress was set up by Yun, Mido’s childhood friend from Seoul, and her husband Lion. Mido initially sees her work there as a stopgap, before she goes on to finish her own degree. But when she discovers that she loves the work, loves the children, and makes more than enough money to support herself she begins to wonder why she needs to return to university at all.

Lion, meanwhile, was a prodigy who graduated from Princeton in three years: exactly the sort of child hagwons are intended to produce. But rather than using his education as a springboard into the wider world, he has found himself running a hagwon of his own; drawn back to the system that launched him. And the trajectory of his own life, the experience of the children in his care, and the inherent injustices, of wealth and background, which the hagwon system perpetuates, leads him to question whether its ends justify its means. “There is a crisis … in our education and what it is meant to do,” he says to the parents of his students towards the novel’s end. “We cannot treat our students as objects to shape and bring to the market.” American Hagwon is a patient, humane, occasionally devastating book about what we ask our children to carry, and why.

• American Hagwon by Min Jin Lee is published by 4th Estate (£25). To support the Guardian order your copy at guardianbookshop.com. Delivery charges may apply.