Today, New York City’s 1.1 million public-school students return to their classrooms—or, in the case of about seventy thousand four-year-olds enrolled in the city’s pre-K program, go to their classrooms for the very first time. It’s been four years since Bill de Blasio bested John Liu, Bill Thompson, Christine Quinn, Anthony Weiner, and others in the Democratic primary—in what New Yorkers might recall, with nostalgia for a more innocent time, as an election that was colorful without being toxic. Among the most popular of de Blasio’s proposals during the campaign was his promise to extend public pre-K, which hitherto had supplied seats for only about half the eligible children in the city, leaving the parents of the remainder to scramble for family care, or to fork over for costly private programs.

Campaign promises are easy to make and fiendishly hard to keep: homelessness, the reduction of which was another signature issue in de Blasio’s 2013 campaign, has increased during the past four years. De Blasio is up for reëlection in November, and, while it seems likely that he will win another four years as Mayor, not all New Yorkers have been impressed by his administration’s performance, which has been marked by investigations into campaign finance and ethics, though no charges were filed. But de Blasio will rightfully be able to point to pre-K as a significant accomplishment: he delivered with a swiftness that even skeptics were obliged to acknowledge, and on a scale that is nationally unprecedented. Two thousand teachers were recruited for the effort, and more than three thousand new classrooms were created in school buildings and approved community centers. The September after de Blasio won the primary, thirteen thousand new pre-K seats were made available to any New York family who wished to apply—rich, poor, or anywhere in between. The places were filled following a thoroughgoing outreach that had taken place in the preceding months. That spring, it seemed hard to find a subway car that was not advertising what struck many parents as an implausibly attractive offering: a safe, cost-free, enriching environment in which their children might garner the foundations of literacy and numeracy, and reap valuable social skills. By September, 2015, more than sixty-eight thousand four-year-olds in New York were the beneficiaries of an extra year of free public education.

The significance of New York’s large-scale investment in pre-K for all can hardly be overstated. Studies have shown that children who have been enrolled in high-quality pre-K programs—in classrooms led by skilled and knowledgeable teachers who engage children in imaginative play and block building, and read to them and teach them songs—have long-term positive outcomes on their future academic and even post-academic lives. One much-cited longitudinal study, the Perry Preschool Study, which began tracking students in Ypsilanti, Michigan, in the early nineteen-sixties, found that those who had been enrolled in a preschool program were, at age forty, more likely to hold a job, had a higher income, and were less likely to have committed crimes than their contemporaries who had not received the same early education. A case for pre-K can be made on the bluntest of economic arguments: some studies have estimated that for every dollar that is invested in high-quality pre-K education—New York spends nearly twelve thousand dollars per student per school year—as much as ten dollars is saved in costs for other government services or expenditures down the line.

Pre-K is hardly a silver bullet for poverty or inequality or persistent economic and racial segregation, in New York or elsewhere. As Dana Goldstein noted in an extensively reported survey of the program, published last year in The Atlantic, the application process is difficult to navigate, especially for parents who don’t have the luxury of time for extensive research. Some excellent non-school-based programs that previously had been private were now eligible to receive public funds, with the result that covetable seats were taken by children whose parents had been able to afford to enroll them a year earlier, at the age of three, in a preschool program for even younger children. Nonetheless, the city’s ambitious embrace of pre-K as a universal entitlement is serving as a model for other cities to attempt their own smaller-scale efforts to tackle early education. This is no minor feat, given a prevailing national skepticism toward the government’s role in education. As Suzanne Bouffard, formerly a writer at the Harvard Graduate Center for Education, notes in her new book, “The Most Important Year: Pre-Kindergarten and the Future of Our Children,” there has long been a wariness about putting very small children in schools, which, she suggests, can be seen as “government overreach during a period of development when children should be at home with their mothers.” Those Americans who decry institutions of public education as “government schools” are unlikely to regard the opening of more public-school classrooms to even younger children as an unassailable advance, no matter what positive outcomes the early-education research shows.

New York’s pre-K initiative, on the other hand, has amounted to an argument in favor of more, not less, government intervention in people’s lives. It was grounded in a populist gesture and an unapologetically progressive conviction: that public institutions can and should serve the communities they represent, and should seek to generate a greater equality among the citizenry. In 2014, de Blasio’s proposal tapped into the kind of embrace of socialist remedies to chronic economic inequality that, a year later, fuelled Bernie Sanders’s Presidential campaign. With his pre-K initiative, de Blasio initially sought, if not to rectify, then at least to make visible some of the city’s income inequity. On the campaign trail, he promised to fund universal pre-K with an income tax on the city’s highest earners, those with incomes of more than half a million dollars annually. This proposal was derailed at the state level; ultimately, the funding for pre-K was found in the state budget without the necessity of levying the additional income tax. This was a disappointment for those whose support for the proposal was grounded not just in the desire to extend educational opportunities for children but in the sincere wish to make the most affluent of New Yorkers contribute more to the commonweal.

One criticism that has been levelled against New York’s pre-K initiative is, paradoxically, that it is too embracing: that it is open to middle-class and wealthy families, as well as to the children of the city’s neediest. Other municipalities in which pre-K has been expanded have made particular efforts to target children from low-income families: last year, Philadelphia opened two thousand new pre-K seats, mostly in areas that had been designated as high-need. Critics have argued that, by making pre-K universal, regardless of means, in New York, families who could afford to pay their way in the private system have become beneficiaries of public funds that might otherwise be spent on their less affluent peers.

But de Blasio and others supportive of the program have argued that making pre-K available to all is fundamental to the program’s intention, and to its success. (This year, the Mayor is starting a new program, known as 3-K: an extra year of preschool for three-year-olds, which is being introduced in Brownsville and the South Bronx, with the intention of expanding it citywide.) There are, after all, plenty of middle-class families for whom the ten or more thousand dollars that they might otherwise spend on private preschool is hardly pocket change; and the availability of pre-K has enabled some parents to return to work who might otherwise have been obliged to stay home. And making an entitlement universal means that it is more likely to become permanent, as Republicans who sought to overturn health-care reforms, earlier this year, discovered.

Furthermore, the provision of public pre-K for all young New Yorkers underscores an important principle, one that in the era of Donald Trump and his Secretary of Education, Betsy DeVos, is only becoming more eroded: the belief that public institutions should be good enough, and widely enough available, for everyone to use them, and to want to use them. To suggest that public schools should be regarded as places for the children of families who can’t afford to send their offspring anywhere else is to devalue what should be a foundational institution of democracy. Universal pre-K makes a universal statement: that public schools should be valued in common, and committed to by all members of a community. At a moment when the nation’s democratic institutions, from the courts to the free press, are under attack, the egalitarian goal of pre-K for all—of anything for all—becomes only more valuable, and only more worthy of cherishing.