In answer to the specific question of validity: no, this is not a valid score (nor are any of the composites derived from it). The various levels of scaffolding that the examiner offered were likely in the way of "testing of limits", which is a way of obtaining clinically-rich information beyond a discontinue or untestable behavior.
With regard to decisions about services and accommodations, this provides fairly clear evidence that he needs some kind of accommodations for writing, in that he has better underlying expressive language than can be demonstrated in a typical on-demand writing task. If this were in one of my evaluations, I would probably have included corresponding recommendations, such as graphic organizer/mind-map (since giving the parameters supported his ability to structure the written product), oral pre-writing exercises (since that is essentially what the examiner did with him, both by structuring and by scribing), speech-to-text for first drafts (scribing), and possibly others, like priming the pump (this may mean a sentence starter or first sentence, or may encompass the oral prewriting mentioned above), or rubrics/checklists for writing.
All of these supports have more to do with executive function and managing anxiety than they do with physical writing.
The way this portion of the eval is written does not suggest to me that the psych is in favor of denying him services.
