Decided to have my son who just turned 5 take the WPPSI-IV to see if he might qualify for Davidson Young Scholars program since I suspected he was gifted and perhaps even profoundly so. His score came back indicating he is actually eligible. His Sunday School Teacher at Church is happy to do the recommendation for him. Will complete the application this month.

It appears that going forward he would need to take another test to qualify for Davidson Academy or Johns Hopkins Center for Talented Youth. I was thinking maybe the WIAT-4? Since this is an achievement test I am considering homeschooling him for 2-3 years and then have him take the test to see where he is at academically. Anyone have any experience with this test? Advice, recommendations?

Why not use the WISC V?

I don't have experience with applying to either institution via this test, but I do have experience with the test itself.

Based on what I can see on the respective websites, it seems to me that the WIAT-4 would be relevant to the Davidson Academy only if you wait until at least third grade to test, since the scores must be no more than three years old, and the school starts at sixth grade. Plus, the performance level needs to be at a late middle school level, so you may or may not want to test him that early for that purpose.

For CTY, you can have him take the SCAT as early as grade two for their programs, which might be useful for your homeschooling efforts.

But if what you want to know is where he is at that point, rather than obtaining qualifying scores for a program, then you could certainly have him take the WIAT in two or three years as a kind of benchmark for homeschooling purposes. It may be helpful to understand that the test is designed to place a student ordinally in the population of their age-peers, rather than to identify their age- or grade-equivalence (notwithstanding the presence of scores with those labels). That is, the percentile/standard score numbers are the highest-quality measures. Related to that, it's best not to readminister it too frequently (best practice is no more than every six months, and typically, quite a bit less frequently than that). So if you think you will need a good administration of it at some specific point in time (say, the summer entering grade five, preparatory to a DA application for grade six), then it might be advisable to plan the previous administration for at least a year or two prior, for maximum utility and minimum retest effects.

Interesting, I had thought for the WIAT-4 it was 5 years for Davidson Academy based on their "accepted tests" page which seems to indicate that individually administered tests are good for 5 years and only the group achievement tests are subject to the 3 year limit. https://www.davidsonacademy.unr.edu/admissions/eligibility/accepted-tests/

To your point though their "eligibility" page seems to indicate that achievement tests are all generally subject to the 3 year limit. I think I should probably go ahead and e-mail them to clarify if individually administered achievement tests like the WIAT-4 are good for 5 years as seems to be indicated on the "accepted tests" page.
https://www.davidsonacademy.unr.edu/admissions/eligibility/

My understanding was that the "standard score" on the WIAT-4 would need to be 145 plus in at least two of the following: reading, math, writing, and total composite. I would guess that this "standard score" is based on age at time of testing? I figured if he was going to take the test anyway it may be better to take it earlier so that I might be able to use the results to help guide my decision making and planning for his elementary education either way.

But yeah you're right that in addition to meeting the minimum achievement test score eligibility requirements he would need to be able to perform at an advanced middle school level in order to eligible for Davidson Academy so even if he were to get a qualifying score on the WIAT-4 in the next few years that doesn't necessarily mean he would be applying right away.

After I posted this I saw that CTY SCAT online test which you mentioned, I might consider that too. Alternatively it looks like CTY accepts ITBS as well which I could even administer at home. I had already been considering doing that anyway as a benchmark to aid my homeschooling as may be needed going forward. I am not sure if my son is ready for formal 2nd grade online school just yet but it is something we may want consider with CTY going forward at some point, perhaps to help prepare him for Davidson Academy longer term.