The private gifted school requires IQ testing for admission to 1st grade. They will do their own testing for $250, but only give you a result of "yes" they can move on to 1st grade or "no" they cannot.
Considering that you need the results before age 6, and the cost of a full WISC plus achievement will be about 10 times what the school is offering to do it for, I would take the schools test for now, and wait for the WISC at age 6. I think that the WPPSI is only worth abuot $250 and you won't get much more info than the Yes/No.
There are other tests, such as SB-V, that you could do now - will the school accept those?
BTW - My sense of things is that
I think that kindergarten will be ok because he will be attending the same school as he is now. It is a private school for the gifted and since they are labelling him as such, I think that they will challenge him appropriately.
this is a bit of a leap of logic. I would ask for examples of what they have done in similar situations. Exceptionally gifted kids are rare (although maybe not so much in Fairfax) and it's rare to find schools that are 'full of good ideas' about how to percieve these kid's readiness levels and accomidate them.
But you are happy with the school so far, that is wonderful!
Grinity