Global Number of Youths Is Highest Ever, U.N. Reports UNITED NATIONS - There are more adolescents today than ever before in human history. Whether they lift their nations to prosperity - or tear them to shreds - will depend, the United Nations warns in a new report, on how swiftly governments can respond to their demands for decent education, health care and jobs. The report, released Tuesday by the United Nations Population Fund, estimates that 1.8 billion people worldwide are 10 to 24 years old. The majority is concentrated in the poor countries of the global south, and there are more than 350 million in India alone. India is also among several countries where the shape of the population is changing profoundly: Fertility rates are dropping, which means a growing share of working-age men and women and a diminishing share of children to care for. That shift, the report asserts, is "opening a window for a demographic dividend," but not without significant investments in preparing its young people to join the work force. "The emergence of a large youth population of unprecedented size can have a profound effect on any country," the report concludes. Whether that effect is positive or negative depends largely on how well governments respond to young people's needs and enable them to engage fully and meaningfully in civic and economic affairs. The poorest countries face the largest share of young people in large part because women continue to bear many more children than in rich countries. In the 33 poorest countries, for instance, most of them in sub-Saharan Africa, nearly a third of the population is between ages 10 and 24. In the world's richest countries, the share is 17 percent. China and the United States each have about a fifth of their populations in that age bracket. Russia's share is 16 percent. Countries that do not tend to their young people now are likely to see higher fertility rates and poorly skilled work forces. The report calls on countries to pay particular attention to the needs of girls and young women, including the need for sexual and reproductive health services. The report is designed to shape the debate around new global development goals that are to be finalized next year. A bulge of young people creates obvious risks. Homicide rates are higher where there are more young people. And there is a strong correlation between the youthfulness of a society and the status of women: Levels of income inequality are higher where youths make up a higher share of the population. While school enrollment has gone up in recent decades worldwide, the report said quality remains so poor in so many schools that about 130 million children stay in school for four years "but never achieve even the minimum benchmarks for learning." Even as the global economic crisis recedes, youth unemployment has continued to grow since 2011, the report finds. The United States is cashing in on another sort of demographic dividend. An estimated 4.5 million students traveled abroad to go to college, according to a separate report published Monday by the Institute of International Education. A fourth of them come to the United States. Correction: November 17, 2014 An earlier version of this article misstated the day of the release of a United Nations report on global youth population. It was released on Tuesday, not Wednesday.