, in my experience, have an official, centralized disability services offices, and you have to be registered with them, they
check out the documentation of your disability, and they
make the determinations and arrangements for whatever accommodations you need. That way, the school is sure that all disabled students are treated fairly/equitably, that the school is fully compliant with the student disability laws (because the people who work in that office are familiar with the laws and regulations, unlike instructors), and your treatment and accommodations are not based on the personal views or opinions of any individual instructor.
At least, that's how it's worked at the schools I've taught at. I'm sure there may be other models out there.