My 10 y/o dd is currently seeing a psychologist to sort out possible ADD or anxiety. The psych told us that lower WMI and PSI scores were common in kids with ADD, but she was surprised that dd's VCI and PRI were so high if that was what was going on. She felt the those two might also be depressed with ADD. She also mentioned that anxiety and ADD can look a lot alike and that she wouldn't be comfortable treating ADD until she was more confident that it wasn't ADD-like symptoms being caused by anxiety.
In regard to your question about being gifted with just one high subtest score, I imagine that opinions would differ, but I'd say yes in a twice-exceptional child, which it sounds like your child may be. I wouldn't call a child with one high subtest on a group test (like the CogAT, OLSAT, etc.) gifted necessarily b/c those aren't technically intelligence tests but more tests of "developed abilities" as the publishers put it. However, IQ should be looking more at intelligence and he is clearly very able in that one area at least.
