We have done our research and while there is no set breed that helps a child with ADD over another (as it is the responsibility and care given that is the main goal) we have acquired a lot of useful information when we do start to look for that special puppy that will get a new home with my nephew.
We have decided that a small to medium mix breed will probably be best... as they tend to have better temperaments and less health issues - not to mention that there is so many of them in city pounds waiting and waiting for someone to come along and love them.
I will post PICS when he or she is found.