Should a person with special needs, physical or cognitive, attempt martial arts? Gee, should they attempt swimming? Theatrical arts? Sports? Maybe we should just put them in a "home" with others of their kind.
Should a person with special needs attempt martial arts? Yes. Absolutely. Exactly what one should expect will vary depending on the disability and the individual. Then again, let's be clear - we all have disabilities. Every single person I have ever trained or trained with has been challenged in some way. That didn't stop us.
I recently witnessed an instructor working with a young girl with some unknown (to me) cognitive disability. He was patiently teaching her how to do jumping jacks. This was a two-step process; first hopping both legs out to the sides and clapping the hands above the head, and then hopping the legs together and slapping the hands on her hips.
Will that young girl ever master a flying side kick, or a jump split two-board break? I have no idea - and neither does anybody else. You just can't know how much can be learned.
Here is what I do know, and I absolutely know this with the certainty that the sun rose yesterday - martial arts training will help everybody.
That young girl may never learn the various moves and turns of Motion 1, our most simplistic form, but the toning of muscles, the repetition of defensive movements, and the constant thoracic exercise (yelling) will help her should she ever need to defend herself - and that is over and above the intrinsic benefits to her health.
Don't let a so-called disability keep you or a loved one from trying a martial art. No one can predict how far you will go, how much you can learn, or how well you will do. What I can predict is this; if you try, you will improve. If you don't try, you won't.