In the first year, its fairly common for that loan to be used to refinance a loan at a really high interest rate from a local money lender, but this does provide some benefit. Now you are paying back a loan at 15% instead of 50%.
Also, a lot of the money goes into paying for kids' education, something that will not have any real ROI in the short term. I'm curious about the mention that education hasn't improved, from what I've seen this doesn't match but I haven't really done a large scale survey.
Its true, some recipients use the money for non profit-making activities (e.g wedding dowries), but my understanding is that many of these would happen anyway with loans at a higher interest rate.
In any event, anyone who thinks that one type of financial instrument is going to solve poverty is mis-guided, but I don't know that these studies really show a lot.