My son got the WISC at 6 years 9 months (school setting) and the DAS at 7 years 3 months (private assessment) while we explored the possibility of learning disabilities. The WISC could not be repeated in that time frame, and in some ways I am a bit sorry we didn't wait longer because there are such wild swings between the verbal scores on those two tests the combination of all results was even more confusing (perceptual/visual remained pretty stable in the bright range and so did working memory in the impaired range, which didn't seem to bother anybody).
I am still trying to figure out if the comprehension subtest of the DAS is even comparable to the comprehension subtest of the WISC, since my son went from 50th to 99.9th percentile between the two tests.
I am also starting to wonder how much tester bias influences all that testing (not necessarily only IQ/achievement, but all neuropsychological assessments), in my most paranoid moments.
