lms, you definitely sound like you have reason to check deeper into dyslexia and/ or something else getting in the way of automaticity in reading and retrieval. It's really unfortunate your school won't assess until third grade; while it's common to wait, the evidence is nonetheless clear that dyslexia can and should be diagnosed and remediated sooner. If there is anything whatsoever to keep pushing on, do keep pushing. In the meantime, the most important thing for him is a proper (Orton-Gillingham based) reading program, so it's awesome that you're already doing that yourself.
As for the testing that's been scheduled, it's possible that the WISC and WIAT will show nothing "below average" with a gifted dyslexic, especially when still in grade 2. But if they do a full set of WIAT reading and writing subtests, it is likely that you will see a pattern of dropping scores as you move from broader skills (like comprehension, which allows many more ways to compensate) to more specific underlying skills (like nonsense words, which are harder to fake).
My DD, tested at that age, was a "perfectly normal" 50th percentile for WIAT comprehension - but that's 2 SDs lower than her WISC verbal comprehension, tested orally. Her scores continued to drop as context was stripped away, so word reading was 16th and nonsense words even lower. Of all her testing (WISC, WIAT, WRAML (memory) and CTOPP (phonological)), the only scores that were officially below "average" (i.e. less than 16th) were three WIAT subtests: nonsense words, spelling and sentence generation. However, the pattern was consistent in all areas of testing: high scores when oral, medium scores with context/ compensation, and low scores when isolated skills were required.
Something to point out to your teachers: a gifted dyslexic will do far, far better with a complex, wordy text than with "easy", isolated words. Teachers assume that if they can do the hard stuff, of course they can do the easy stuff - but they never check.
