Dysgraphic DS13 has the same problem with composing that you describe. He has always struggled with finding words to write but has profound insights verbally. This written/verbal disparity makes most teachers assume that he is lazy and disinterested.
Yesterday I was scribing an English assignment for him in which he had to compose a sentence using a grammar rule (colon; possessive; correct use of numerals, etc.) This assignment should take about 5 minutes but he really struggled! "Okay, just think of any sentence with a possessive. Anything." (Me waiting, pen poised, for 2 minutes.) "Just name a possessive. Any one. Then put it in a sentence." Still nothing for about a minute, then finally, a simple sentence. We did this about 10 times. It's hard to believe that simple drafting is so difficult for him but it truly is.
I think the drafting struggle is probably more a product of his expressive language disorder and by his extremely slow word retrieval speed. The expressive language deficit was identified in his recent CAPD testing and the low "rapid naming" was revealed in dyslexia testing (the CTOPP.) DS' rapid naming was in the 1st percentile for speed!
I think both DS' slow word retrieval and expressive language issues cause a logjam for writing that is only exacerbated by the struggle to physically write.
I suspected that DS was dyslexic as well as dysgraphic but I never dreamed he had an auditory processing deficit (which is related to expressive language problems), mainly because he has super sensitive ears. Do you have any concerns about auditory processing of ryour DD? Or dyslexia? The slow speed you reference could be related to very slow or inefficient word retrieval that underpins dyslexia. The signs of dyslexia for gifted kids are dysgraphia, poor spelling, poor oral reading and difficulty with sounding out nonsense words.
Oh and btw, the requirement of "below average scores" is nonsense. The scores must show a significant ability/achievement gap for a diagnosis.
