It's hard to summarize, so read the whole thing. But he is calling for a closer look at the evidence and the application of RCT [randomized control trial] standards. Here is an excerpt:
First, the fact that a technology has been scientifically proven in isolation–such as a certain fertilizer proven to raise crop yields–does not mean that it will improve people’s well-being amidst the complexities of real villages. Recent research by Esther Duflo, CGD non-resident fellow Michael Kremer, and Jonathan Robinson shows that fertilizer use is scientifically proven highly effective at raising farm yields and farmers’ profits in Kenya. But for complex reasons very few farmers wish to adopt fertilizer, even those well trained in its use and usefulness. This means that this proven technology has enormous difficulty raising farmers’ incomes in practice. The gap between agronomy and development is very hard to cross.
Second, it is not sufficient to compare treated villages to untreated villages that were chosen ex-post as comparison villages because they appear similar. Many recent research papers have shown this conclusively. A long list of studies conducted over decades showed that African and other children learned much more in schools that had textbooks than in schools that appeared otherwise similar but did not have textbooks. Paul Glewwe, Michael Kremer, and Sylvie Moulin evaluated a large intervention in some of the neediest schools in Kenya (ungated version here, published here). Schools that received textbooks were randomly chosen from an initial pool of candidates. The problem: Children did not learn more in the treated schools than in the untreated schools.
Chris Blattman comments.