Something to keep in mind... If his boss has already determined he is constantly underachieving or has negative impressions of him, it is going to be very difficult to change that viewpoint and have people see the new changes without a big change. Some managers may detect the poitive changes and try to help, but I have also seen too many times that many people tend to hold on to earlier opinions of who you are regardless of whay you do. Any effort he makes has to be internally driven, and he may have to figure out how to keep up with positive changes even if initially people around him are not able to support him in ways that will help him hold on to those changes.
(Now if only I can figure out how to get a coworker to understand why he is constantly passed over for promotions or why some - most - of my team don't show him the same level of leadership and respect as others on my team... But I have given up on that person for the most part... If after 5 years, he does not get it, I doubt he will suddenly wake up and figure it out and I am tired)
