Over the past century, three approaches have been advocated to escape the consequences of widespread poverty, rapid population growth, environmental problems, and social injustices. The bigger pie approach says: use technology to produce more and alleviate shortages. The fewer forks approach says: make contraception and reproductive health care available to eliminate unwanted fertility and slow population growth. The better manners approach says: eliminate violence and corruption; improve trade, the operation of markets, and government provision of public goods; reduce the unwanted aftereffects of consumption, such as environmental damage; and achieve greater social and political equity between young and old, male and female, rich and poor.

Providing all the world s children with a high-quality primary and secondary education, whether through formal schooling or by alternative means, could, in principle, support all three of these approaches. Education provides economic benefits, builds strong societies and polities, and improves health. It is also a widely accepted humanitarian obligation and an internationally mandated human right.

The good news is that over the past century, access to education has increased enormously, illiteracy has fallen dramatically, and a higher proportion of people are completing primary, secondary, or tertiary education than ever before. But huge problems remain. About 115 million children of primary school age are not currently enrolled in school. Most are illiterate and live in absolute poverty; the majority are female. Some 264 million children of secondary school age are not currently enrolled. Large educational disparities exist within and between countries. The quality of schooling is often very low. Moreover, demographic projections suggest that developing countries will have 80 million more children of primary and secondary school age (typically 6.17 years old) by 2025 than now, that is, an increase of 6% to 1.35 billion.

In 1990, the global community pledged at the World Conference on Education for All in Jomtien, Thailand, to achieve universal primary education (UPE) and greatly reduce illiteracy by 2000. In 2000, when these goals had not been met, it repeated the pledge, this time at the World Education Forum in Dakar, Senegal, with a target date of 2015. The UN Millennium Development Conference in 2000 also adopted UPE by 2015 as one of its goals, along with the elimination of gender disparities in primary and secondary education by 2015. But even the modest UPE goal now looks unlikely to be achieved by 2015 at the current rate of progress. An estimated 335 million school-age children will be missing primary or secondary school in 2015; of these, an estimated 118 million will be absent from primary school. About one in five of these children will never enroll in or attend school.

About 115 million children of primary school age are not currently enrolled in school. Most are illiterate and live in absolute poverty; the majority are female.

Given this series of missed targets, what is feasible? Estimates are that UPE can be achieved by 2015 if the global community invests another $6 billion to $35 billion per year, on top of the approximately $82 billion developing countries already spend each year on primary education. This article argues that this sum is not only affordable but essential. It also argues that the UPE goal is not ambitious enough: the world should aim for, and can achieve, high-quality, universal secondary education, possibly by 2015 but certainly by the middle of the 21st century. The price tag for achieving this goal might be an additional $27 billion to $34 billion per year starting now, on top of the approximately $93 billion developing countries already spend each year on secondary education. However, the obstacles are not just financial. Leaders need to devise and implement policies that will make educating children unquestionably worthwhile, in the eyes of parents and everyone else.

• In 1900, estimated primary GERs were below 40% in all regions except northwestern Europe, North America, and Anglophone regions of the Pacific, where the ratio was 72%. But by 2000, the estimated global primary net enrollment ratio (NER) the ratio of the number of children in the official primary school age group enrolled in primary education to the population of the primary school age group had reached 85% globally. The NER is a stricter standard than the GER, so the achievement is all the more remarkable.

• In developing countries, literacy tripled in the 20th century, from 25% to 75%, and the average years of schooling more than doubled between 1960 and 1990, increasing from 2.1 to 4.4 years. That figure has risen further since 1990.

• The number of students enrolled in secondary school increased tenfold in the past 50 years, roughly from 50 million to 500 million.

As for data quality, developing countries have begun to participate in international measurements of educational status in greater numbers. Even so, more statistical measures of schooling have been defined (for example, net and gross enrollment ratios, attendance rates, completion rates, average years of attainment, and school life expectancy) than are well supported by reliable, internationally comparable, and comprehensive data. The UNESCO Institute for Statistics, Montreal, maintains the highest-quality data.

• Roughly 380 million children are not enrolled in school (28% of the age group, typically 6).

• More than one-fourth of these children are absent from primary school (with the rest missing secondary school).

• Of school-age children who enter primary school in developing countries, more than one in four drops out before attaining literacy (World Bank, 2002).

• The populations farthest from achieving UPE are typically the world s poorest. In sub-Saharan Africa, the primary NER is only 63% far below the 96% in Latin America and the Caribbean.

• Girls education falls short of boys education in much of the world. While enrollment rates sometimes do not differ greatly, many more boys than girls complete schooling, especially at the primary level.

A systematic global analysis remains to be done, region by region, of how much gender, urban or rural residence, and high or low income contribute to differences in children s educational opportunities and achievements, but we know they interact. In India in 1992, for example, the enrollment rate of boys ages 6 exceeded that of girls by 2.5 percentage points among children of the richest households; the difference in favor of boys was 24 percentage points among children from poor households. Girls are more disadvantaged relative to boys in poor homes. The boys from rich households had enrollment rates 34 percentage points higher than those of boys from poor households; the gap in favor of rich girls compared with poor girls was 55.4 percentage points. Wealth gaps in enrollment greatly exceeded gender gaps in enrollment.

Spending on primary education varies widely among developing countries, ranging from $46 per student per year in South Asia and $68 in sub-Saharan Africa to $878 in Eastern Europe and Central Asia (see Table 2). Spending per student in secondary education shows a similar disparity, ranging from $117 per student per year in South Asia and $257 in sub-Saharan Africa to $577 in Latin America and the Caribbean.

More money for education usually results in better education, but exceptions to this pattern are informative. A 2001 study of Latin American primary education showed that Cuba led in test scores, completion rates, and literacy levels. The lowest fourth of Cuban students performed above the regional average in third and fourth grade mathematics and language achievement, although most nations of the hemisphere spent more public money per student than the less than $1,000 spent in Cuba. This example suggests that policymakers, who are acutely aware of the competing demands on resources, might do well to investigate how some countries have achieved so much with only modest funds.

How much could countries afford to spend? The World Bank estimates that the low-income countries, with a population of about 2.4 billion, had a combined gross national income (GNI) of almost $1 trillion in 2000 (with an average annual per capita income of $410). The incremental cost of $34 billion $69 billion per year would be 3% of their GNI, assuming they shouldered the entire incremental burden without any external help. The low- and middle-income countries, with a population of nearly 5.1 billion, had a combined GNI of nearly $6 trillion (with an average annual per capita income of $1,160). The incremental cost for them would be about 0.6-.2% of their GNI.

Of course, if the richer countries shared the cost, the burden on the poorer countries would be less. The GNI of the high-income countries was $25.5 trillion out of the entire world s $31.5 trillion so an extra $70 billion per year would be less than 0.3% of their income. Official development assistance (ODA) in 2003 was $69 billion, the highest ever in nominal and real terms. However, this amount was only 0.25% of donors combined GNI. Moreover, it was well short of the average of 0.33% of ODA/GNI achieved in 1980 and of the United Nations ODA target of 0.7%. Thus, the incremental cost of $34 billion $69 billion per year could consume up to the entire pie of recent ODA.

As public funds are limited, it is natural to ask: Is education the best use of the marginal dollar of government expenditure in a developing country? Should that dollar be spent on education rather than health, physical infrastructure, or applied research? Unfortunately, we know no convincing answers to these questions, even if the "best use" is interpreted narrowly as economically most efficient. Credible models to evaluate the trade-offs for human well-being between education and other sectors of public investment appear to be lacking. The same fundamental lack of knowledge applies to the trade-offs between primary and secondary or higher education. However, the difficulty of achieving universal education is about a lot more than money.