This is a tough one. I think it depends a lot on what you are looking to get out of it. If you want it for advocacy purposes, or to get your child into a gifted program, school placement, acceleration etc, then obviously you would want to do the testing before those things happen. if its just to know, and you are happy with the school situation as of right now, then it's not as dire. No matter what, I don't think any IQ test will to tell you more about your child that than you already know, though it might certainly make you feel more justified about her apparent giftedness.
I know there is a lot of back and forth on this forum (and in general) about the 'right' time to test, as far as age and accuracy of testing. a lot of people say that four is too young, wait until six or seven because IQ tends to stabilize at that point...but if you have a reason to do it earlier, then waiting several years isn't necessarily an option. My opinion is that a 7 year old could theoretically be just as disagreeable as a four year old in any given testing circumstance. And if the number you get back from a four year old doesn't reflect their 'true IQ', then why are there tests like the WPPSI in the first place?? Seems kooky too me.
random tidbit: I just learned that the new WPPSI-IV has extended norms, which the WPPSI-III did not have - which is very good for a gifted pre-schooler, in my opinion. Especially because hitting ceilings is/was one of my bigger concerns with that test vs. the WISC. Food for thought if you do decide to go ahead with the testing.
The last consideration I would mention is cost - private testing can be expensive - hundreds of dollars...if that is prohibitive to you, then clearly waiting until the district will test for free would be a big advantage there.
Honestly, I think it's just a matter of weighing your options and going with whatever you feel most comfortable with...there is no wrong answer. Best of luck!
