What spurred you to get an assessment?
I'm not sure what to make of the coding, but want to strong discourage you from prepping from any future IQ tests. If you are going to devote the time and resource to going through testing, it's in your best interest, long term, to get the most accurate result possible - that means no prepping. I know that you had the best of intentions, but I want to mention it for the lurkers who are reading your post and thinking 'I should try that myself!'
Even if his processing speed is just fine working memory limitations can make showing a child's strengths really hard at school. I also notice that he is quite a different kid in his home environment than he is at school or with the tester. Does he have anxiety challenges? It's hard to pay attention when one is frightened.
He certainly is bright, but his scores don't reflect a kid who is so far out there in brightness that socializing would be affected. Some kids who are fearful get test scores that aren't accurate.
I guess you could find a reasonably kind adult your child doesn't know and send your kid to the stranger adults house to do more coding pages and have the adult get some timed scores and see if that's the issue.
I know with myself, I was somehow able to get the very best behavior out of my child by not pushing his buttons. I didn't do that consciously, so it took many years to try and figure out why things were so different in different environments. Maybe he and I are so alike that I just fell into it by treating him the way I would want to be treated in his situation.
That isn't the cultural norm. Kids are expected to adapt to environments, not the other way around. One parenting book that help me with this is
http://www.amazon.com/Transforming-Difficult-Child-Workbook-Interactive/dp/0967050758As far as afterscooling, I would suggest you follow his lead. If he likes doing academics and it's fun for you, then do them at home by all means, but spend some of your attention helping him with his interpersonal challenges. The workbook was helpful with that for me.
Smiles,
Grinity