I'm not sure about the symbols or most of the interpretive terms--it's been too long since I've administered or scored a WIAT.
A caution about grade equivalent scores though: they don't equate to grade level ability. I always have difficulty communicating this one, but here's a link and a quote that might help
"What the grade equivalent score actually measures is how typical students at the grade level specified would perform on the test that has been given. In other words, the grade equivalent of 10.4 does not indicate that the 4th grade is doing of doing 10th grade work. Rather, it indicates that the 4th grade student has performed as well as a typical 10th grade student would have performed on the 4th grade test. If the student is performing on grade level, that is a 4th grade student taking the test in the 10th month of 4th grade receives a score of 4.10, then it simply indicates that he/she is performing right at the average for other 4th graders in the norming sample, which is the 50th percentile and 50th NCE."
link for quote I wouldn't worry too much about it being the tester's first time with WIAT if she has administered WJ before. The general administration techniques are the same. Scoring the writing and the oral expression would be new, but otherwise I wouldn't expect much impact. The unknown for me is how appropriate the test is for gifted students at this age. If Dottie were around, she could probably address that....{sigh}.
Perhaps go into the meeting with an eye to discussing whether the test has anything to offer in terms of suggesting accommodations that might be helpful, but not as if it is a determination about whether or not acceleration is appropriate. Presumably all of the determining factors that led to the decision are still in place. You might gently remind the rest of the team of that if they get too stuck on this one test. Good luck--I know going into these meetings is always nerve-wracking
