In my kids, IQ and grade level equivalents have no relationship, while the scaled scores of index scores correlate with one another, at least within a standard deviation or so. Grade level equivalents appear to be produced by a random number generator.
Attempting to make correlations with grade level equivalents in our case are a fruitless endeavor.
Not a random number generator. Regression & curve smoothing. But still with little relationship to real-world instructional levels. Which is why the APA and NASP specifically dis-recommend the use of grade equivalents in assessment reporting and interpretation.
I know this. I should have maybe worded it "as if generated..." The GE does not correlate well across subtests, nor does the same scaled score equate the same number of grades ahead for a given subtests across the years (so a 130 in kindergarten is very different than in 4th). DS has identical scaled scores on different subtests, yet the GE is wildly different. Looking at his GE's on the latest round of WJ (which, granted, will qualify him for special ed), range from -2 to +14 of his current grade level, which the SS's range from low end of average to +78 points above the lowest score.
Clear now.
The scaled/standard/all z-score-derived scores correlate with each other because all the psychometric work goes into making sure they do. That grade equivalent tables exist at all is an unfortunate concession to age/grade-locked teacher-thinking, which is an outgrowth of our warehoused approach to formal education.
One of the few times I find some utility in age/grade equivalents is when attempting to describe the cognitive development of extremely low functioning students (e.g., teens with skills at an infant level). Mainly because most people have no sense what that many negative SDs means. And because the number isn't nearly as important as what they can and can't do to interact with their environment. But just as with the other tail of the curve, there are so many developmental asynchronies and gap/splinter skills that an equivalent still doesn't provide a particularly accurate picture.
It's odd that we ever expect equivalents to be legit, when you consider that there -may- be one or two items at each grade level (whatever that might be) on a NRT like the WJ. Obviously, there is no way they can be comprehensive.
