My child was just diagnosed with ASD. During the evaluation he had to take another WISC-V (he took it twice before, ~2 years between each). I am really surprised by how much his scores fluctuate between assessments. For example, on the same subtest he would score 17 and then the next time 7. Or vice-versa his score would go from 14 to 19. In the end he averages out around the same FSIQ. Is this fluctuation typical? Or does it have something to do with ASD? How much variability is "normal"?

PS. I am not concerned about his scores, I am just curious.

Good to hear you've finally received some answers on your child (if this is the same one we've discussed a few times before).

It depends a little on the type of task. At the simplest level, though, yes, it likely does have something to with ASD. I find generally that the cognitive scores of students with ASD don't really stabilize until a bit later than NT students--often well into adolescence. The ability to demonstrate their skills on demand seems to require some executive functions that may be among their lagging skills, and moments of particular rigidity can interfere with optimal performance, especially on timed tasks.

And at the same time, some subtest score fluctuation is also to be expected in the ordinary course of retesting. The reliability of subtests is not anywhere near as high as that of composite/index scores, which is, of course, why the FSIQ is consistent, but the subtests appear less so.

Thanks, Aeh! Yes, the same child and, yes, it's a relief to finally have a diagnosis. Although, now I need to figure out what to do about it (resources? support?) which is a little overwhelming. But overall he's doing great: he's 3-4 yeas ahead in math and 1-2 years in humanities (except spelling just like the rest of the family, LOL). His struggles are definitely non-academic.

As to the index scores they fluctuate too, but definitely not as much. For example, PSI ranges between 123 and 96 (SS 7-17, Co stays 11-13), FRI between 141 and 128 (only MR fluctuates), WMI 107-122 (DS always 10, PS 12-18). He has the least variability on tasks that he is consistently bad at (VSI). His strong scores are the ones that fluctuate, but since they never co-fluctuate, the FSIQ stays roughly the same (+/-3 points).