Thank you for the thoughtful responses. They are helpful.
We have a Great Dane. Even well trained, I know well enough to not tether
myself to a dog let alone a child. Simple GD leaning will knock you off balance.

I am no stranger to therapy animals. I know my son needs something more.
Some background: My first dog (as an adult), I trained as a family pet/obedience dog - a level headed, crowd pleasing 4.5lb Chihuahua. He helped my "raise" my babies and we worked together as an AAT team in the community until he developed cataracts and was no longer comfortable in our busy household. He now lives in the lap of luxury in a retirement community with grandma and grandpa who've begged to have him for years.
My instincts told me that my son could benefit greatly from AAT and social interaction in an accommodating setting so we signed him up for 4H at the age of 5 and he got his own therapy animal - a tiny Jersey Wooly rabbit. She was a miracle worker and claimed my son as hers. She made it clear that my instincts were right and that beautiful and beneficial animals would be a part of our lives because they benefit our family in many ways.
My son and I raise and show nationally competitive rabbits state-wide and across the country. He specializes in one breed, I in another.
My 10 yr old also raises and shows Pastel Call ducks, Rhode Island Reds, and a small Toggenburg dairy goat herd. He also has fancy pheasants. Other animals on the ranch (that belong to us) are Sumatras, a few bantams, and heritage turkeys. That is his thing; he really connects with, understands, and retains information about animals. Like some are uncannily good with numbers or musically talented (like my autistic BIL), my son has a knack with animals and is better with them and more knowledgeable about them than most adults.
My boys have done animal chores, since age 2, and learn to train their animals, from age 5, under my guidance. That is not to say that my 10 yr old will be able to give commands to a dog in an episode but many adults can't do that, either. I still have to mull this SD thing over.
Anyway, when the kids were younger, I trained both my dogs to pass the TDI test which we failed due to my own foolish errors during testing. Tip: Don't dremel you dog's nails right before the test.

Shortly after that, I realized that I had to give all my attention to my family after my 3rd child began exhibiting troubling symptoms and did not retake the test.
We only own one dog but there are ranch dogs here, too. They are not trained the same as my Dane, but they don't bother the kids.
That is our animal background. I have no desire to have another dog because of the years of training involved in getting them "just where I want them" UNLESS it is one that is trained to do specific tasks that will help my son or myself.
A SD at school would not be an issue. The teacher is all for it. No hesitation there. My children go to a very unorthodox public school. K-8, lots of teachers, 35 students in the entire school. It is it's own school district. I know that at least one other similar school in the area actually has more than one dog at their school. These are country folk. A dog is good. A dog that does a job to help a human is invaluable. Accommodations will be made if needed.
As I've been mulling over the thought of a SD, I've wondered if the dog would be more for my son or for me. I have issues of my own that I'd rather not be specific about here in which a live, interactive, specifically trained creature could help me function. Still, I am not set on anything just yet.
If I got a dog for
me, I would definitely want it trained to find family members for the safety reasons stated above. Keeping me on task, using touch stimulation, for time sensitive issues would be great as audible reminders like alarm clocks or phone calls seem to not mean much to me. I don't know what to call that. I'm not good with realizing how much time has passed because I get obsessed with things. Gosh, that sounds dumb but it's true.

*sigh* So much to consider.