I had/have a blurter. When I talked to him about it, he said he just needed to get out what he knew. He didn't want to forget what he had to say. With his teacher's permission, I gave him a pad of large, lined sticky notes for his desk. He could write down whatever he wanted to blurt out, and the teacher would look at it sometime during the day. He got out what he wanted to say, and his teacher acknowledged that he knew the answers, even though it wasn't instantaneous. He only kept up with his sticky notes for a couple of months, but it helped a lot.
