I don't have much more factual data to add ;), but thought that I'd add my anecdote. Both of my dds have taken the WISC. Dd#1, who is a consistently high achiever in school and has successfully been grade skipped, scored about 5 pts higher on her GAI than FSIQ b/c her processing speed was low-avg. However, her other three indices were all well into the 90s (percentiles). She has a very good auditory memory, which is what the WISC WM index tests (short-term only). All she has needed accommodations for in school is time. She can do high level work & remember what needs to be done (pays attention and often doesn't need to use her planner to remember the assignments much to my chagrin!)
Dd#2, on the other hand was 18 pts higher on a GAI the first time she was tested with upper 99s on the Verbal index and PRI, and avg scores on WMI and PSI. The second time she was tested the GAI was about 9 pts higher than FSIQ, but WMI and PSI were still a lot lower than the other two. She is my very erratic achieving child and the much lower auditory memory score does seem to impact her learning. She isn't very good at paying attn to what the teacher is saying and often doesn't remember the material b/c she never heard it in the first place. Although she, at times, has scores on both ability and achievement that are PG, I doubt that we will be grade skipping her given her more erratic achievement, lack of attention to detail, and more uneven profile.
