From what I understand most students arrive with documentation from their high-school (usually brought by their mothers, of course).  Others have notes from their doctor.  (We don't actually get to see the documentation, just a form instructing us what they are entitled to from our Accommodations Office...and a stern warning that it is our legal obligation to do as we are told.)

I don't know all of the details but I also understand that there are government subsidies for tuition support, technology (such as computers), and that there are even tax benefits for claiming a disability in certain cases.  If true this may help explain the huge explosion in these cases most recently.

Also I've noticed that since the counselling office has grown so large that the beast must now be fed, and that they are actively encouraging more people to sign-up for accommodations, private testing, etc.