This is a question that has been asked (and ‘answered’) for decades. Since 2011 ODI, with the support of the Bill and Melinda Gates Foundation, has been collecting case studies to try and create a more systematic answer to this question through their Development Progress program. At the half way mark of the project they have released a nifty video to showcase some of the success stories they have collected so far.
The program will continue to operate through to 2015 with the aim of becoming “a hub for contemporary debates in development through partnership, convening and public engagement.” Keep an eye out for more cases of success (and failure) from the program in the coming months.