Hello!
I will share with you our experience over the past 6 months in testing our son and maybe you can use some of what we learned as you begin your journey.
He was 4.5 years old when we tested him for entrance to a gifted school. He was tested on the WPPSI-III for IQ and the Woodcock Johnson for achievement. A few weeks ago, at 4.10 years old we did a different achievement, the WIAT II to see how his achievement scores might differ over the almost 6 months.
Our experience with the testing was that he did not complete the tests in the hour or so they were promised to take. Each test took about 3- 3.5 hours. The psychologist was very sensitive to the fact that we were testing a 4 year old and made sure to take lots of breaks for playtime. This slowed things down a bit. The other big factor was that the more they know, the longer they go, and in some cases they can go for a very long time. In fact, we actually came back extra days to make sure he wasn't burned out. I think this worked extremely well. I am very confident that she got the best from my son. I would be very surprised, since you already suspect he is gifted, (and parents are the best at identifying) if your tests were limited to the one hour.
As far as the tests themselves go, as mentioned above, I am not sure you can get good testing in the higher ranges for 4 year olds. For the WPPSI-III - our son hit the "ceiling" in 5 of the subsets - telling us that we really don't know his real IQ. It could be that the "ceiling" just happens to be at his actual level, or it could mean if he had the opportunity, he could have gone higher. Then there are those, including Davidson YS program that say that WPSSI-III scores tend to be inflated in some young children. They actually require a 150 because of this while most all other IQ tests they accept are at 145.
Another thing to consider when deciding to wait longer is that research shows that the Processing Speed IQ Score tends to follow actual developmental milestones regardless of levels of giftedness. So a younger child who scores very high in their VIQ and their PIQ may find their PSIQ significantly lower. Waiting may help close that gap a bit so it doesn't negatively affect the score.
And the achievement tests are even harder to apply to 4 year olds. Our first test, the WJ, only norms for grades at Kindergarten level and above. That is why we chose the WIAT II the second time around. That test you can norm at Pre-K but only for a handful of the areas. Neither test was able to give us age-scaled composite scores because certain areas don't have testing materials for their age including spelling, numerical operations, broad reading and math to name a few. In fact, the psychologist who gave us the WIAT II said she had to given him subtests that are not traditionally given to a child his age and that it wasn't the "proper" way, but she had no choice given that his age material would barely delve into his reading and math skills.
We were able to get age and grade equivalents which we are told are not all that reliable but did help frame our argument for radical grade skipping which turned out to be a futile.
Another factor to consider if you are doing achievement tests is that writing and oral expression skills might be somewhat lower than the other scores since they "seem to reflect age appropriate motor skills and brain development rather than areas of decreased achievement." (Taken right from the tester's report)
I would not recommend doing these so young unless they are required for admission or you plan on using them to advocate for special accommodations based on academic achievement.
We, like you, are very new at this but the past 6 months we have learned so much.
Best of luck to you.
