Yes, it is possible to compare the WISC with the WIAT. The psych is also correct that it should be used with caution, as it used to be a routine (but unfortunately not sufficiently evidence-based) approach to diagnosing learning disabilities (the aptitude-achievement discrepancy model). I still think comparing cognitive and achievement profiles has value, when used in the proper context. There is ongoing discussion and research about newer formulations of LD diagnosis that do so, such as the pattern of strengths and weaknesses model, and the cross-battery model.
Not stopping when time ended is not dissimilar from exceeding time limits, if the resulting responses were more accurate than those obtaining at the moment time expired.
Good to hear that the district is starting off from a supportive stance.
If you would like feedback on scores, I think most people would be receptive to responding. You may wish to think about your level of comfort with posting his data on a public forum (sometimes posters delete the scores and other sensitive information after enough other posters have responded). There are others here whose children are also 2e GT/ASD, whose contributions may be helpful to you.
