BARACK OBAMA likes to call education “the currency for the information age”. His presidency has brought a big shift in America’s priorities, devoting more effort and resources—and an extra $2 billion—to children who have not yet started their formal schooling.

That is part of an international trend. South Korea plans to extend their early-education provision for all three- and four-year-olds this year. Turkey has ambitious plans too. Pre-school education was long neglected. “90% of the brain develops between the ages of zero to five, yet we spend 90% of our dollars on kids above the age of five,” says Timothy Knowles of the University of Chicago. That is now changing. Academic studies, including in neuroscience, have highlighted the long-term effects of experiences in a child’s early years.

The most recent report by the OECD, a rich-world think-tank, in 2009, found that 15-year-olds who had attended pre-schools for more than a year performed better (even accounting for socioeconomic background) than those who had attended for only a year or not at all. In Belgium, France and Israel pupils educated at pre-schools had much higher reading scores than those who had stayed at home.

Yet establishing the precise link between time in pre-school and later achievement is difficult. Even defining the term is difficult: it is also known as nursery, pre-K, and early-child education, and the children range from tiny tots in some countries to six-year-olds in others. Measuring its quality is hard. The amounts taxpayers devote to it vary, as does the balance between state and private provision. National attitudes to the right way to spend early childhood years differ. Too much pressure too early may set children up for failure later, notes Alan Smithers, a British education expert.

Israel starred in the OECD report (see chart) and since a wave of social protests in 2011 has put effort and money into further reforms. Aliza Marriott, a public-relations consultant living in Jerusalem, is proud that her children in pre-school are “much more advanced” than she was at their age. Yet the key to success, if any, is unclear. Measuring other data, a report on pre-school availability and teaching standards called “Starting Well” (compiled for the Lien Foundation by the Economist Intelligence Unit, our sister company) placed Finland top (it scored direly in the OECD study). At least 98% of children aged five or six are in pre-school education there. Finland also dominates the overall league tables for education performance, so perhaps the scope for improvement is slight. Other enthusiastic providers of pre-school education like Sweden, Norway, France and Belgium and Denmark do not score particularly highly on attainment in later education, whereas Japan, which combines early-years provision with a fiercely competitive exam culture, excels. So too does South Korea, where the state until now has provided under half of pre-school places. So pre-school is no panacea, says Andreas Schleicher, who oversees the OECD’s big triennial PISA report on educational attainment. “Drilling children” in early years does not lead automatically to learning gains, he says. The greatest success in pre-school provision probably comes from reaching the children who need it most, from poor, neglectful or unstable families. But this is hard. Britain’s Sure Start scheme, introduced in 1999, proved popular: motivated parents liked the extra stimulation for their children. But it failed to reach some of the neediest children, whose parents could not or would not ensure their attendance. Elizabeth Truss, Britain’s minister for child care, wants tougher qualifications for pre-school teachers, but less regulation of how they work (a row is raging over her proposal to allow them to look after up to six children each, instead of four). Early-years education spending in Britain is just below the average of developed countries, at an annual $6,493 per student (New Zealand spends twice as much).

Some of the fastest changes, however, are happening where local politicians have free rein. Michael Bloomberg, the mayor of New York, is opening its first “cradle-to-kindergarten” school later this year for 130 under-fives from poor families, an idea copied from a similar scheme in Chicago. Pre-kindergarten enrolment has increased in New York from 40,000 a decade ago to 58,000 in 2012 and the mayor wants to add 4,000 full-day places in the most deprived areas of the city. Early-years learning is not a magic solution to the elusive modern quest for social mobility. But it can help focus tiny minds on aspiration and bigger ones on how to support it.