DD has around that spread but it's between PRI and PSI. PRI was 147 without extended norms and PSI was 94. In her case you can see it because she is slow with written work and hates writing. She has executive funcitoning issues related to ADHD and has very little sense of time. She can't even really eat a meal in a timely fashion because she spends so much time talking and fiddling with things. Today she spent 20 minutes in the shower making us late for school, then screamed at me "I don't have an internal clock, OK!?" DS7 said "yes you do, it's called your brain" (which I thought was hilarious coming from him because he's almost as bad). So my point is that we can see it in everyday life. DS also has a gap but not as big (maybe 30 points between PRI and PSI) and the neuropsych who assessed him said it could cause problems in that he's ready for higher level concepts but will appear "slow"...not a huge deal but accommodations may need to be made. If these aren't things you're dealing with, then I don't think you should be concerned with the score.
If he has coordination issues, look into Developmental Coordination Disorder/Dyspraxia. Wikipedia has a good page and describes how these issues tend to tie together. Kids with DCD often have poor working memories (in terms of remembering what they are doing) and are scattered, and have spatial deficits.
