Valid reasons to appeal?

I just was formally diagnosed with ADD as a second semester senior. I have since started taking medication and have felt myself become much more focused and attentive in class. I feel my GPA, a 3.4, does not match my intelligence in part due to the fact that I have had trouble focusing in class. Now I finally know what was causing my inattentiveness. My SAT is a 2010 which is very high in relation to my GPA. Do I have a legitimate reason to appeal some admissions decisions?

If the diagnosis was a complete surprise, then you possibly have a reason to appeal. If you had an idea before applying to colleges, then not really. It may not even change the perspective or decision of the colleges but obviously, it never hurts to try. Talk this over with your GC and see what s/he says.

No, this is not a reason to appeal. ADD diagnosis only really helps if they have a change to compare your performance before and after medication, so a diagnosis at this time will not allow them to do so.