What's the test for? DD was tested with the WPPSI at 4 1/2 and did not want to play along, not at all. The write-up has a couple paragraphs detailing how she hid under the table, cried, required 37 snacks, and refused to answer the easy questions at all (then finally got into it when the questions got harder). The scores were still fine for what we needed them for, which was admission to a particular private school and her ADHD evaluation.
But, I will say that when she took the WISC this spring, at 8, and actually cooperated (and maybe even enjoyed herself), every single score went up more than 1 SD.