Typically, the evals covered under health insurance won't include extensive educational achievement testing, which you will need for looking at writing challenges, but you may be able to get parts of what you need done. E.g., In addition to your thought regarding executive functions, I'd particularly want to pursue the speech and language angle for possible expressive language disorders. And yes, it is possible to have extremely high verbal cognition, and yet struggle with expressive language. Thinking is not the same thing as communicating.
It sounds like he can integrate knowledge and concepts, and communicate them, when he is speaking out of a very deep pool of background knowledge and context, but that without enough context to organize a smaller pool of data, he struggles to create his own framework. (Notice also that science labs and experimental write-ups have standard structures.) Something like a biography would be particularly challenging, as there is more ambiguity about the natural organization of biographical information. Does he do better when scaffolded with a graphic organizer of some sort? E.g., a timeline-based bio would have three or so anchor time points: origins, period of historical significance (when this person did or was whatever makes them historically important), end-of-life. Depending on how low the product was supposed to be, one could have additional subcategories, like under origins, you might have family history and birth, childhood and early education, and other influential experiences, people, or circumstances. If he can complete and apply a graphic organizer successfully, that might suggest that the challenge is principally one of executive functions. He'd probably benefit from explicit instruction in the classic five-paragraph essay (and all its upward and downward extensions), to give him a standard algorithm for written expression.
BTW, I just have to say that 5-7 typed pages is not typical third-grade fare, even for a long-term project. Were these typed or handwritten pages?
