Great question - which I knew some answers, but can at least 'bump' you up!
I would ask the school psychologist to look at his old scores and to start him as high up as possible. Maybe it isn't possible to choose the starting point, but my son's school did his WISC IV, and it seemed to take much much longer than expected because they started him below grade level on the subtests - they were used to testing kids with learning disabilities, and had no idea of how high he was going to go, even though a report was avialible to them from his private testing from a few years ago.
In other words, if they have to start him a grade level, so be it, but try to see if the psychologist will agree not to start below grade level...toward that end, maybe I would send in a few samples of his work (in his own handwriting if possible) that demonstrates that 8th to 10th grade level for the school psychologist to review before the testing starts.
Best Wishes,
Grinity
