I have heard it mentioned for kids with CAPD, but I have never heard of a specific case where it was done. We did teach our son sign language when he was 3, because he was speech delayed. He clearly wanted to communicate, but didn't know the words to use. He picked up about 100 signs quickly, and it worked for him as a communication tool. His mainstream first grade teacher uses sign in class. She asks the kids to use it to signal her they need water, go to the bathroom, or need help with work, or have an issue with something happening in the class. It's been very helpful for my son.