I don't know the answers to all of your questions, but I'll take a swing at those I do have some input on
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And for those children who have taken multiple IQ tests, how are the scores usually compared among the tests?
First, I must state that my dd#2 is a very erratic person. Her achievement scores on the NWEA MAPS (achievement tests given at school) vary by as much as 40 percentiles every time she takes the tests.
That aside, she has taken the WISC-IV twice, the SB-5 once (under less than ideal circumstances), and the RIAS. Her WISC scores were over 20 pts apart on the same test one year apart (higher the first time at 7.5 than at 8.5). Her SB-5 score was about 30 pts below her WISC-IV score from the year prior and about 10 pts below her WISC score from the test given at the same time. Her RIAS score was uninterpretable b/c the scores w/in subtests varied too much.
At worst, she is bright, but not gifted (a hair above 1 SD above the mean). At best, she is in the 99.9th percentile. I don't have any idea if these tests just aren't foolproof accurate or if there is some problem with my dd although the psych who tested her the second time tells us that she ruled out LDs/a 2E situation.
My general understanding is that the score for one person shouldn't go up or down by more than maybe 10 pts or a few percentiles depending on the age of the person. IQ scores from a younger age are less stable in general. If 150 is within the margin of testing error for his earlier score, it seems entirely possible that he would score that high if tested again. Then again, he could also score lower than before by a few points.
And, which might be a better IQ test for a child who answers questions without hearing/reading all the instructions?
Reading all of the instructions shouldn't be an issue on an IQ test in that they are verbally administered. If he tunes out and doesn't listen to the instructions, that is another issue. All of the tests require him to listen to instructions to a similar degree. I believe that there are more "teaching" or practice tests on the SB-5 than the WISC-IV. Basically, there are more opportunities to practice the piece that you are about to be tested on before your performance counts on the SB, so that may be of some benefit if you are uncertain as to whether he would just start going w/out fully understanding what is being asked of him.
