Well, this is tricky because it is a multilayered answer, and I mean no disrespect to anyone here but unless you live with kids with disabilities you honestly don't understand how it can be.
And a lot of disabled kids do not have the capabilities of being good TO dogs. A child who can not understand how to be good to dogs due to disabilities, should definitely have a different type of breed (if it is mild behavior issues) and maybe no dog at all if serious behavior issues, unfortunately. I just had to get that out there, and I don't mean "you" the OP because it sounds like your child has the ability to have a loving relationship with an animal, as are mine
. There is such a variety of disabled when it comes to kids. One of my son's peers bites animals and nothing makes him stop. So, no he should not have a dog no matter how much he wants one. Anyway, I don't want to be a blanket ambassador for saying yes, special needs works with (insert any breed) without specifying the special needs person must be suitable for a dog as well as vice versa. That said...
I have 3 kids 12, 10, and 7. The 10 and 7 year olds are disabled. 10 year old has autism and very serious hyperactivity. 7 year old has CP and maybe autism. Hard to tell how much is due to losing oxygen at birth and if he would have had autism regardless. On paper, I have no business owning the 2 year old and 8 week old working lines that I have. However in my opinion they are the best dogs for my family because they are stable and great with the kids and also fulfill my wants and needs from a dog as well (IPO, protective of the home and kids, partner).
That said a few things really need to come in to play for this to work. First and foremost a trusted breeder who not only breeds genetically sound dogs but understands their dogs and how to place them. Then you, the owner. You must be willing and able to hire a breed savvy trainer to help you when you are not sure of things. Whatever you think you know about the breed, be willing to let an established trainer guide you. Look up a local IPO (now IGP) club and either consider joining ( I go 2 Saturdays a month it does not have to be too time consuming) or if not hang around a bit, ask for opinions on breeders and trainers.
If all those things come to into play nicely it can absolutely be done. I don't know much about ASL GSDs, but I would let the breeder and what they produce steer me more than whether it was a Working Line or German Showline.
Good luck and if you would like to PM me about more specifics and ins and outs of special needs kids and GSDs and life in general, please feel free!