How is that tester bias? It seems like a fairly direct explanation of problems or weaknesses observed? It's possible your Child didn't gel with the tester, and that impacted their attention. I have watched my daughters being tested and their performance absolutely was variable between subtests, they were more interested in looking out the window than doing the test on any subtests they didn't find engaging. Though that was muh more a problem with the wisc/WPPSI than the sb5 which is much faster paced...
