Randomized trials like these—that is, trials in which the intervention is assigned randomly—are the simplest and best way of assessing the impact of a program. They mimic the procedures used in trials of new drugs, which is one situation in which, for obvious reasons, a lot of care has gone into making sure that only the interventions that really work get approved, though of course not with complete success. In many ways social programs are very much like drugs: they have the potential to transform the life prospects of people. It seems appropriate that they should be held to the same high standards.
Here are the responses to the article. In Banerjee’s response to the comments, he writes,
I should have said more about what is probably the best argument for the experimental approach: it spurs innovation by making it easy to see what works.
(With thanks for the reference to Tyler Cowan of Marginal Revolution)