First of all, I am not limiting processing speed to the simple measures on IQ test such as the WISC IV. I am thinking more broadly of processing speed as reflected in daily life.
I know that some people, including Dr. Reynolds (RIAS), do not believe that processing speed has a place in measuring intelligence. However, after close encounters with both super fast and profoundly slow as well as fairly normal speeds in my own kids, I cannot but conclude that processing speed has a definite, lasting and cumulative effect on achievement as well as the development of intelligence.
For example, all other things equal, a brisk processing speed allows a student exposure to a larger wealth of ideas, including vocabulary. One reason why DD11 is significantly behind DS11 in standard measures is that DS can fit so much more into the same hours in the day. He can easily finish reading several books on a single day whereas DD may read one or two on a good day. If you multiply that by even five to ten years, the difference is tremendous.
Of course, I don't believe that processing speed is the most important measure of intelligence - only that it makes a significant difference.
