I'm not familiar with the WIAT, so I can't help you with specific questions, but fwiw my ds12 has LDs and his scores jump around quite a bit on individual achievement tests (WJ-III) in spite of the fact that he performs extremely well at school. What helped me understand his achievement test results was to look at the specifics of what each subtest measures and how the test is administered - for example, on the WJ-III some subtests are administered by giving an oral prompt, some require reading etc. Some subtests are timed, some are not. Some subtests require a written response, some require an oral response. When I made a chart and grouped subtest score vs response type or prompt type etc, very clear patterns emerged that make sense with respect to his LD.
Just looking briefly at the scores you've posted, most of them seem really a-ok, with math computation possibly an area of weakness. I suspect that any test labelled "fluency" involves a timed component, and when you see a lower score in a timed test with a kid it's quite possible that the reason for the lower score is simply because the test is timed and has nothing to do with the child's mastery of the subject. There can be many reasons that any of the test scores are unexpectedly low, including the timed test. I'd suspect ADHD could make it difficult to finish a test in a given period of time; my ds doesn't have ADHD but the act of handwriting causes him to have a challenge with timed tests.
You should be able to get clarification from your tester - but in the meantime, it might also help to try to google around and find a list detailing what the specifics of each WIAT test are.
Best wishes,
polarbear
