FWIW in my experience having official diagnoses does help. Whenever I get push back I pull out the official dx paper/reports/evals and push-back tends to melt away....I'd be nervous not having it as they are always trying to find a way to take away my son's accommodations by saying he doesn't 'need' it anymore.
This is another good reason to have an official diagnosis, and having the correct diagnosis is going to help when you're advocating, because even with the official diagnosis, many of us have to advocate like crazy and be able to show examples of how a diagnosis is impacting our child - having the incorrect diagnosis or missing a diagnosis isn't going to help with advocacy.
polar
