I have not read Dr. Ruf's book, so I can't comment on that. However, if we are talking about a grade-level achievement test, then the GE's are in fact pretty meaningless. If a 2nd grader gets a GE of, let's say, 9th grade, that means that the 2nd grader got the same score as a 9th grade student would if that 9th grade student took the same (2nd grade level) test. Frankly, it seems ridiculous to even calculate this sort of grade equivalent. Who cares what a 9th grader would score on a 2nd grade test?
Even on Achievement Tests that cover many grade levels (e.g. WJ-III or WIAT-II, etc...) you still need to take GE's with a grain of salt. There are two reasons for this: One, the tests have very few questions per grade level. Two, if your 2nd grader gets a GE of 6th grade, let's say, that means that they have achieved the same score as an AVERAGE 6th grader (from an average school) would. For most parents of GT kids, we would never want our child to be performing at the level of an average Xth grader from an average school.
Not sure if that helps, but no doubt other people can chime in and clarify anything that I have not explained well.
