I think the problem is that he was not yet four years old at the time of the test. I gather he will be six towards the end of this year? Once he turns six, he can take the WISC-V, instead of the WPPSI-IV, which is what the publisher advises for high-cognitive children (they have overlapping age ranges, both including 6-0 to 7-5).
As far as achievement tests go, I would probably lean toward the KTEA-3, out of the options listed, if you want a sense of his real range, though I'm sure you could get scores sufficient for access to resources out of any of the KTEA-3, WIAT-III, or WJIV. The WIAT is a bit limited for kindergartners (no reading comprehension, for example), and I don't find the WJ as young-child-friendly (it's relatively long, for one). You should be able to derive core reading, math, and written language scores in six subtests on the KTEA, which I think strikes a nice balance between informative and brief (important for small, wiggly people). Also important because very high achieving students (particularly very young ones) often take much longer to complete testing, as they have to go through many more items to reach their challenge level.
