DD's lowest score was coding as well (it was 25th percentile, or an "8", on WISC IV). Compare that to GAI 150.

She was impaired on every aspect of EF (the 7 or 8 "boxes") on the BRIEF.

Only difference between her and your DS is that she does not have Aspergers.

Sometimes she is helped with a timer, for instance she is sometimes overwhelmed w/ her math homework. Sometimes I set a timer and say "see what you can get done in 20 min. then you can stop". If she knows that she only has to work for 20 min. it seems to help. But other times, knowing there is a time limit makes her extremely anxious. For instance timed math fluency tests.