My son may be similar to yours. He is 5 and we just got back his scores. He took WPPSI III, his PIQ is 150, his FSIQ is 144. He is quite good in math and he got 160 on Math on WJ-III which is much more than they ask for. Needless to say we plan to apply to DYS in January.
I say if your son is good in math then the assessment test may be worth to do it at this age. I consider my son being very good in math but not THAT good. KWIM? His score took me by surprise. My guess is that extensive math knowledge at this age is very rare and your son my do really well on the test and get qualifying score with a few points to spare. Good luck
