My Dd who has ADHD did the WPPSI not the WISC, so no WMI, though her WMI was high on the SB5... But she absolutely had issues in the WPPSI where she couldn't handle the boredom of the amount of easy work required at the start of a subtest before she worked up to her level, there were a couple of subtests where she was looking avidly at the content of the first few items and barely glancing or giving any thought by the time she was closer to her actual level, instead by then she was spinning her chair from side to side and looking out the window. One subtest was spoiled completely.
Comparatively on the SB5, which has routing questions to bring a child in at roughly the right level, she was much better focused because it was more consistently engaging (better tester too).
A good tester should note in their report if the child was distracted, impulsive, not well engaged with certain parts of the test.
