Truscifi,
the WPPSI and it's sub tests look the same, what my DS was tested with for the first time, to see if he would qualify for gifted program at public schools. It did take a little longer, maybe an hour I am estimating.
I think that it is the standard under 6 years of age. However, because your DS was almost 6 at the time, I would wonder if the test was limiting to his capabilities. I know my DS hit several ceilings and he was not even 5 at the time.
Knowing what I know now, I would have requested the SB-5, which has much higher ceilings even at such a young age.
I would definitely request the achievement test to go with the IQ. To me it is a very important part in trying to understand these little kids minds.
