In my experience working with clients with special needs (in my previous university writing center), I have always found it important to check in with them first to see how I can make their learning environment best suited to their needs. It is imperative to remember that they are adults, just as myself, and should not be talked down to. It can be especially harmful to make assumptions about people with special needs, because this takes away their power to make their own decisions and have their voice be heard.
It is also critically important to have patience and empathy when communicating with persons with special needs. For instance, I have worked with clients with special needs who have difficulty focusing on tasks. Rather than pushing them refocus on what we are working on in the limited time we have together (during a timed appointment), I try to give them the space they need to learn comfortably and ask if they have any questions about the material we are covering. When speaking about people with special needs, it is very important to always use person-centered language. This ensures that the person is always being put first, before their special needs.
Hopefully this helps :)