I never said it’s not legal, I said it’s being tested in court. There’s litigation pending. I have no idea how that case is going to turn out, the court may end up ruling that it’s fine and Disney may end up following suit. The rules for education are different and for the workplace are different.
There are different rules for the workplace and schools. The section on public accommodations makes (IIRC) three mentions of prohibited documentation. They involve mobility devices, accessible seating and service dogs. For the most part, the ADA doesn't want businesses asking for documentation before allowing a person to use the accommodations that the ADA requires.
A business can ask for some assurance that the person using the mobility device can drive it; a driver's license is okay, but a verbal assurance that is not contradicted by observation is allowed.
A business is prohibited from asking for documentation that a person needs accessible seating. But this involves physical modifications for seating that are covered by the ADA. If the business runs out of the required amount of accessible seating the next person who requests it is out of luck and the ADA has not been violated.
The third (and the one that is cited in Six Flags' lawsuit (I need to check that)) is the prohibition against asking for documentation of service dogs. Allowing service dogs is expressly required by the ADA and allows two questions to be asked - whether the animal is required because of a disability and what work or tasks the animal is trained to perform. There are also protections for the business if the animal is not behaving as a service dog and causing disruption.
The first two - mobility devices and accessible seating - are distinguishable from something like line accommodations. The third - service animals - is the closest. But service animals are expressly covered by the ADA and, to be honest, that provision is wildly unpopular and abused. I would not want to be the lawyer asking for an extension of that provision to prohibit asking for accommodation for standing in lines at a theme park.
I believe there is a DOJ opinion saying that a line accommodation "may" be required, but those opinions expressly state that they have no legal effect and are not binding.
The fact is that - from what I've seen - the law is very unsettled in this area. I don't think Disney's lawyers know for certain how the Six Flags litigation will turn out, but my bet is that Six Flags will win. Just my opinion, which can definitely be wrong.
I'm just addressing documentation, not what's reasonable accommodation or what questions can be asked.