I will say that is takes all of the scores combined to get a Full Scale IQ. That is why DYS requires both an academic assessment and an IQ.
Thankfully DYS isn't looking only for kids with 99.9 Full Scale IQ - LOL 'cause then I wouldn't be here - no one else was willing to explain to me that even with an uneven profile and OG FSIQ, my son is unusually gifted.
I think regression towards the mean is most of what we are seeing. If Processing speed were very highly associated with deep abstract thinking abilities, then there would be less scatter.
From the point of view of advocacy, I think having 120 or more Processing speed helps a child fit into most school's notion of 'what a gifted kid should look like.'
I think that having fast processing speed is a lovely addition to High Verbal and Perceptual. It helps people think deeply 'fast.' I suspect I'm very fast but more bottlenecked in the WM department, so go easy on me when we meet in person and I've forgotten your name! Here I can 'search' and read up on folks before I try to answer posts - wish I could do that in real life! I also notice that I can type faster than my inner voice can speak, so internally I'm processing even faster than my awareness. When I first started posting here I was quite often surprised at where my posts ended up!
Smiles,
grinity
