Shashi Tharoor is India’s Minister of State for Human Resource Development. His most recent book is Pax Indica: India and the World of the 21st Century.

NEW DELHI – One of the more difficult questions I found myself being asked when I was a United Nations under-secretary-general, especially when addressing a general audience, was: “What is the single most important thing that can be done to improve the world?”

It’s the kind of question that tends to bring out the bureaucrat in even the most direct of communicators, as one feels obliged to explain the complexity of the challenges confronting humanity: how no imperative can be singled out over other goals; how the struggle for peace, the fight against poverty, and the battle to eradicate disease must all be waged side by side; and so on – mind-numbingly.

Then I learned to cast caution to the wind and venture an answer to this most impossible of questions. If I had to pick the one thing that we must do above all else, I now offer a two-word mantra: “educate girls.”

It really is that simple. No action has been proven to do more for the human race than the education of female children. Scholarly studies and research projects have established what common sense might already have told us: if you educate a boy, you educate a person; but if you educate a girl, you educate a family and benefit an entire community.

The evidence is striking. Increased schooling of mothers has a measureable impact on their children’s health, education, and adult productivity. Children of educated mothers consistently out-perform children with educated fathers and illiterate mothers. Given that, in general, children spend most of their time with their mothers, this is hardly surprising.

A girl who has had more than six years of education is better equipped to seek and use medical advice, to immunize her children, and to be aware of the importance of sanitary practices, from boiling water to washing hands. A World Health Organization study established that “in Africa, children of mothers who have received five years of education are 40% more likely to live beyond the age of 5.”

Moreover, a Yale University study showed that the heights and weights for newborn children of women with a basic education were consistently higher than those of babies born to uneducated women. A UNESCO project demonstrated that “each additional year of a mother’s schooling reduces the probability of the infant mortality rate by 5% to 10%”

The health advantages of education extend beyond childbirth and infant health. AIDS spreads twice as fast, a Zambian study shows, among uneducated girls than among those who have been to school. Educated girls marry later, and are less susceptible to abuse by older men. And educated women tend to have fewer children and space them more wisely, facilitating a higher level of care; women with seven years’ education, according to one study, had 2-3 fewer children than women with no schooling.

The World Bank, with its typical mathematical precision, has estimated that for every four years of education, fertility is reduced by about one birth per mother. The reason why the Indian state of Kerala’s fertility rate is 1.7 per couple, whereas Bihar’s is more than four, is that Kerala’s women are educated and half of Bihar’s are not. The greater the number of girls who go to secondary school, the Bank adds, the higher the country’s per capita income growth.

Moreover, women learn from other women, so uneducated women often emulate educated women’s success. And women spend more of their income on their families, which men do not necessarily do (rural toddy shops in India, after all, thrive on men’s self-indulgent spending habits). And, when educated girls work in the fields, as so many in the developing world must, their schooling translates directly into increased agricultural productivity and to a decline in malnutrition. Educate a girl, and you benefit a community.

I learned many of these details from my former colleague Catherine Bertini, a 2004 World Food Prize laureate for her tireless and effective work as head of the UN World Food Program. As she put it in her acceptance speech: “If someone told you that, with just 12 years of investment of about $1 billion a year, you could, across the developing world, increase economic growth, decrease infant mortality, increase agricultural yields, improve maternal health, improve children’s health and nutrition, increase the numbers of children – girls and boys – in school, slow down population growth, increase the number of men and women who can read and write, decrease the spread of AIDS, add new people to the work force, and be able to improve their wages without pushing others out of the work force, what would you say? Such a deal! What is it? How can I sign up?”

Sadly, the world is not yet rushing to “sign up” to the challenge of educating girls, who consistently lag behind boys in access to schooling throughout the developing world. An estimated 65 million girls around the world never see the inside of a classroom. Yet not educating them costs the world more than putting them through school.

Certainly, there is no better answer. Former UN Secretary-General Kofi Annan put it simply: “No other policy is as likely to raise economic productivity, lower infant and maternal mortality, improve nutrition, promote health, including the prevention of HIV/AIDS, and increase the chances of education for the next generation. Let us invest in women and girls.”

Read more: Gender Gap Report

The Global Gender Gap Report provides a framework for capturing the magnitude and scope of gender-based disparities around the world. The index benchmarks national gender gaps on economic, political, education- and health-based criteria. Check where your country ranks:

The opinions expressed here are those of the author, not necessarily those of the World Economic Forum. Published in collaboration with Project Syndicate.

Image: A young girl sits inside a classroom in New Delhi REUTERS/Mansi Thapliyal