I'm sure that aeh will be along soon to give you more detailed information, but I can tell you a little. The FSIQ is a composite calculated from all of the subtests, so the same subtests that brought down the VSI and the WMI will also have brought down the FSIQ.
The type of memory measured in the WMI is not the same sort of memory as you describe being one of your son's strengths. It is really about short-term memory and how much you can hold in your brain at one time. The reason it is tested is because it impacts how well you will be able solve complicated problems that require you to hold all the pieces in your mind at once as you manipulate them.
The impulsivity is associated with ADHD, but it is also associated with being a 4-year-old boy. He may just need a little more time to mature. Again, aeh will give you more reliable information, but you may want to wait until he turns 6 before you do further testing, as that will open up the possibility of using the WISC, which is probably a more reliable instrument.
The Wikipedia articles on the
WPPSI and the
WISC are as good a place as any to get an idea of what the subtests are and what the different indices represent.
