It really does work! One year I had a sweet little boy in my class with Down’s syndrome. His mom and dad taught him sign language early because they knew he would have difficulties with oral speech. She read to him hours each day as well. One of the most well behaved child with special needs that I have worked with. It’s hard for the parents to discipline their children with special needs because they tend to feel sorry for them and falsely believe they can’t do more. It’s just a different type of learning.
That would be a perfect use for sign. I wonder if there’s ever been a study on that type of use.