While there are less subtests at the lower ages, they are also much "easier" to score extremely high on. For example, early readers can hit scores over 200 on the WJ for some very basic skills! This is also true for the math. In that regard, you probably won't have a great picture until your child is more "school aged", but you can get one that does tell you your child is indeed statistically rare.
Best wishes!
I agree it's probably easier to get higher scores early on but I think you get pretty good idea where your child is by looking at the grade level equivalents. I wish we could get the test done every year just to know where it is. That said if my son's grade equivalent for math is 3.8 it doesn't mean that there are no gaps. The test can test only so much without being way too long.
At 5 you need to know much more than basic reading to get 200. I must admit though that our son did worse on the reading test than we expected (around 3rd grade scores). It makes me wonder what he did on the comprehension part.
Let me write down a few scores and grade equivalents to give you a better idea.
Broad Math 3.8 160
Calculation 3.8 143
Math Fluency 2.9 137
Applied Problems 4.1 169
My son's fluency levels were usually lower than the rest of his scores. The scores are timed and I think that's where going to school helps. You can be a great speller but if you write slowly you won't fit too many sentences in a given time frame.
Spelling 4.0 162
Writing Fluency 1.9 124
I don't know if you want to talk to your son about it or if the time pressure would just make him more nervous. In math you can ask for another problem if the given one is too hard.
