Ok, let me re-phrase my question. If the directions on the school assignment said "Write a paragraph answering this question", would it be a well-organized response that made sense? I think you have to try to separate out whether he could write a decent response if he knew that more than one sentence was expected. If he can not, you still don't know whether it's impaired language that's causing the problem or if it's poor EF (or both). If you find a good language test that is accurate with gifted kids, and it comes out fine, then you can probably assume it's a written expression issue caused either by poor instruction or poor EF.
I think he can do this, at least at grade-level, if he follows a specific format. His writing skills are considered strong but what I see is his writing does not appear to have matured in several years. This could just be a motivation or attitude issue--I just don't want to assume anything after reading so much here!
Then again, not to generalize too much I do remember from teaching that *most* (not all) gifted boys did not write as well as gifted girls, in high school. So maybe I don't need to question every little thing and assume pathology.
