Here is a link to Wikipedia on the WISC-IV. I read through it and it is accurate and much easier to understand that the professional testing sites.
http://en.wikipedia.org/wiki/Wechsler_Intelligence_Scale_for_Children
To interpret any standard score test (SS) you need to know what the standard deviation (SD) is. David is exactly one SD below the mean on Processing Speed, and is almost 2 SD above the mean on Perceptual Reasoning. This is likely a stat sig difference but whether or not it is meaningful depends on the circumstances.
I just "upped" a thread in which I responded at length about the meaning of test score spread. The thread was started by mistmouse but I give an example of my two kids as young children that shows that the interpretation of score scatter can be very tricky.
I think that your son is slow in motor skills because he is 1 SD below the mean on Processing Speed. However, there are many ways to get this score, some of them problematic and others, not. For example, if he tends to be a perfectionist who want to be "right" no matter what, he will lose all time bonuses and lower his score. See particularly my comments about my offer to "lower" ex-difficult child's (non-meaningful) split because he was getting every time bonus available. HOWEVER, he also had (and has) some Obsessive Compulsive Disorder (OCD) traits that if I tapped into, i.e., made him concerned about "correctness", he would have slowed down.
It is for reasons such as the above that experienced clinicians want the "observational information" regarding how a child approaches tasks as much as they want the scores. Unfortunately, if your SD is trying to use testing vs your child, that sort of information will never be discussed.
One the other hand, no one ever scores, "too high." It's always real (unless it is curricular-based and the child has been coached.) So David's Perceptual Reasoning is an individual strength as well as above the 95%ile in relation to the general population.
PR includes
Block Design - children put together red-and-white blocks in a pattern according to a displayed model. This is timed, and some of the more difficult puzzles award bonuses for speed.
Picture Concepts - children are shown rows of pictures, and are asked to find a common bond with one picture in each row.
Matrix Reasoning - children are shown an array of pictures with one missing square, and select the picture that fits the array from five options.
Picture Completion (supplemental) - children are shown artwork of common objects with a missing part, and asked to identify the missing part by pointing and/or naming.
These are closely related to what used to be called non-verbal IQ on all WISC series prior to the IV.
The only thing that jumps out at me in terms of his achievement scores is math calculation is relatively low in comparison to other scores. So is vocabulary. This suggests to me that either he is not being exposed to an enriched curriculum OR if he is, he is not making use of it. That is possible--been there done that with ex-difficult child. He and his sister went through the same system through 8th grade--often having the same teachers, and she came out a whole lot better educated than he. You can lead a horse to water....
Of course, David's scores are only individually low--they are dead-on average in comparison to the norming population, so the SD is not going to think much about them.
IF the low processing speed is valid, you might see problems in completing class work as quickly as other children--That said, there can be many other reasons for not finishing class work on time, including low motivation, ADHD, fine motor problems, etc.
My gut feeling is you have not reported any major school problems that appear to be related to the test scores. However, remember that the test scores are a one (or two) time snap shot and that problems can appear as children age and school demands increase.
I hate to keep repeating the same thing--but SOMETIMES splits are hugely important, and unaddressed, would lead to major problems (as for my easy child) and other times they are artifactual and without real meaning (my ex-difficult child).
So the unsatisfactory answer is, IT DEPENDS....
Martie