Now that he's on medication for ADHD, is it reasonable to retest him since he scored so high on his verbal portion of the WISC III? I think he may be gifted.
If your son it the kind of student who needs to be academically challenged, the ADHD symptoms he exhibits may, in fact, be his quest for stimulation and challenge. If your son truly has ADHD and was tested before he began taking the medication, it would be entirely reasonable to have him retested to get a better picture of his true abilities. This is especially true if you feel the medication has helped him. If the psychologist who tested your son in the first place is not open to this, get him tested elsewhere -- preferably by someone who knows giftedness when they see it.