There are 13 categories that one can be classified as being a SWD (Student with Disability) and, for the most part, there are a PLETHORA of SWD that people don't even know that they are classified as such. I can presume that you may be speaking of the "obvious" ones--blind, hard of hearing/deaf, wheelchair, Downs.
Speak to them as you would speak to anyone else. They know that they are different and a 90% of them do not being "labeled." I explain to them that EVERYONE has a deficit in some area so EVERYONE is "disabled" if we are to make that distinction. Being a Special Ed Specialist/Advocate, I make sure that they do not use their classification as a crutch and I also let them know that they are different just like everyone is different in some shape, form or fashion.