The Idealist: Jeffrey Sachs and the Quest to End Poverty, by Nina Munk, Doubleday, 260 pp., $26.95.

The simplicity of Jeffrey Sachs' formula for ending poverty made it ideal for a successful advocacy campaign. All the problems of poverty had technological fixes, the Columbia University economist argued: bed nets to prevent malaria-spreading mosquito bites, wells to provide clean water, hospitals to treat curable diseases, fertilizer to raise yields of food crops. Ending poverty, therefore, was just a matter of raising enough money to pay for the package of these technical solutions to the poor's problems. Sachs would demonstrate his ideas by deploying these comprehensive tech fixes in a dozen or so "Millennium Villages" in Africa. Success would build on success to scale Sachs' fixes up throughout the continent.

The Idealist, Nina Munk's brilliant book on Sachs, chronicles how this dream fell a bit short of reality. Munk, a contributing editor at Vanity Fair, follows Sachs around as he tries to make all this happen. But she also goes out on her own to the Millennium Villages. She visits two villages repeatedly: Dertu, in the ethnic Somali region of Kenya's arid north, and the more centrally located settlement of Ruhiira, Uganda. Munk thus makes us see the villagers as real people, not stereotypes.

The technical fixes turn out to be anything but simple. The saga of Dertu's water wells is illustrative. Ahmed Mohamed was the local man that the Sachs project put in charge in Dertu. Soon after starting his assignment, Mohamed had to order a crucial part lacking for the water wells' generator. It took four months to arrive, and then nobody knew how to install the missing part. Eventually a distant mechanic arrived at great expense. A couple years later, Munk found Mohamed struggling with the same issues: The wells had broken down again, the parts were lacking again, and again nobody knew how to fix them.

A little over a year later, the Millennium Villages blog celebrated Dertu's wells as "the most reliable water supply within the region." But by 2011, the wells had run dry altogether due to a drought—not such a surprising occurrence in an arid region.

Such examples multiply in Munk's book, showing that the purely technological answer to poverty was far from the simple solution Sachs said it was. Alas, technology does not implement itself, it requires implementation by real people subject to widely varying incentives and constraints in complex social and political systems.

Munk shows successes as well as failures. Sachs' project spent $1.2 million on health in the other village, Ruhiira, including hiring two doctors and 13 midwives. Many fewer mothers in Ruhiira are now left to their own resources to give birth, and the prevalence of malaria has fallen drastically. But the difficulty achieving the successes and the frequency of the failures contradicted Sachs' original promises. Munk found herself chronicling a rising chorus of criticism in the past couple of years. Three months before the release of Munk's book, Foreign Policy also published a harsh critique of the project, offering negative verdicts from virtually everyone else in development.

Perhaps most revealing about the big aid debate that Sachs launched is what finally unleashed this wave of criticism of Sachs. Like Al Capone being convicted of tax evasion, Sachs' promise that aid would deliver an end to poverty wound up being convicted on a lesser charge: not doing evaluation properly. The critics pointed out that any positive trends in the Millennium Villages would have to be compared with the positive Africa-wide trends in health, access to clean water, and overall development. Sachs had not set up the project in a way where this comparison could be done reliably. For example, his team had not collected any data on any similar villages that were not a part of Sachs' project, which would have made it possible to compare what happens with and without the Millennium Villages treatment.

The critics in Munk's book and in the Foreign Policy article now only hope that Sachs' project could show what kinds of very specific technical fixes could deliver some modest payoff for their immediate objective, such as midwives decreasing unattended births. The NYU economist Jonathan Morduch, for example, told Foreign Policy that Sachs' "big-package approach is an anachronism relative to the ideas that development economists have gravitated toward….Today's typical projects are narrow, easier to evaluate, and pitched as part of a layering of independent interventions. A sanitation project here. A school intervention there." Sachs' set-up failed to deliver the kind of evaluation-friendly project that could show today's development economists "what works" to get some very focused (and relatively modest) results in the target areas.

Sachs' actual objective for the Millennium Villages—to show that aid could achieve the end of poverty—does not even merit a mention by Sachs' critics today. This idea is apparently so distant to today's development economists as not even to be worth refuting. The big aid debate that Sachs initiated is now really over.

That said, this movement toward small programs with small goals doesn't really get the development problem right. The verdict of the big debate—that aid will never be the engine of development—should make it clear that aid and development are two different topics that should each have their own separate debates. If today's development economists will talk only about what can be tested with a small randomized experiment, they confine themselves only to the small aid debates and leave the big development debate to others, often those appealing to anecdotes, prejudice, and partisanship. It would be much better to confront the big issues, like the role of political and economic freedom in achieving development.

I am obliged to disclose any bias, so I should say a word about my own history with Sachs. In 2005, when I wrote a negative review of Sachs' book The End of Poverty, I became identified for years afterward (with rising unwillingness) as the antithesis to Sachs' thesis, a never-ending debate—aid can end poverty! no it can't!—that played itself out in dueling books, blogs, media quotes, and syllabuses.

Eight and a half years later, I take no pleasure in the defeat of Sachs' big ideas, especially as this failure involves the sufferings of those who were the subjects of the Millennium Villages Project. And Sachs does deserve some positive recognition: He was and is a very gifted and hard-working advocate for compassion for those still left out of the considerable progress that has happened in development. But his idea that aid could achieve rapid development and the end of poverty was wrong, and it's time to move on. It's time to debate what really does matter in development.