I don’t think I’ve ever asked for or granted a change of final grade in a class, but I’ve been on both sides of grade changes for individual assignments. Sometimes it’s just plain an error, and sometimes it’s a judgement call on how much something is worth, and the student can make a good case for it. In fact, sometimes when I’m grading something, and an answer is right on the line between two grades, I’ll give the lower grade, but decide in advance to change it to the higher one if the student asks about it. If a professor is even halfway decent, the worst that can happen from disputing a scoring is that you’ll get some extra discussion from the instructor and understand the subject a bit better.
I have, however, gotten requests to change a final grade. I had one student once in an intro astronomy class, who did absolutely terribly. I had surveyed the students the first day on their science and math background, even though I didn’t intend to use any math in the class (it had no prerequisites), and this student claimed that she had had calculus. But she kept complaining that there was “too much math” in the class (a complaint not shared by the students who claimed to have nothing above arithmetic). At the end of the semester, she even went so far as to make an appointment with the department head, and complained to him that the class was supposed to be an “easy A”, so obviously she should get an A in it. Neither the head nor I are quite sure how he managed to avoid laughing her out of the office.
[bb]Clothahump**, did you tell that story before on the SDMB? Something about being curled up under your desk reading, while the conversation was taking place? It was a great story then, and still a great story reading about it again.