I got sooo tired of kids blurting out and interrupting each other, that one day I stopped the therapy session and drew a picture on the back of a piece of paper - face with a thought bubble, and another with a speech bubble, and then I drew a little clock at the bottom. Then the following conversation ensued:
Me: "When I ask you a question, you use your thought bubble to think about the answer. You think and think (and I drew a line under the pictures from one face to the other) and then when you have the answer you use your talking bubble to tell me. Some people need more time to think than other, and that's ok. Let's pretend I ask you, "Johnny," a question. You think and think about your answer (I trace over the line again) but before you get to tell me, "Jane" shouts out the answer (here I use my finger to erase a spot in the dry erase pen line, which breaks the continuous 'thinking line.') So Johnny, did you get to finish your thought?
Me: "Did Johnny's brain get to find the answer by itself?"
Me: "Did Johnny's brain get a chance to work?"
Me: "So tell me, how will Johnny's brain ever get a chance to learn if it never get to find the answer?"
Kids: "...ooooooohhhhh" *insert lightbulb going off here*
Me: "If I hear all four of your voices talking at the same time, will I be able to understand what you say?"
Me: "Right. My brain panics and stops working. It can't understand all that information at once. This is why we teachers have you guys do things like raise your hand, put your thumb on your heart, or show me 'same' if you agree. It lets me - the teacher - know that you have an idea or you agree with the other student without you having to interrupt and make your friend's brain stop working. You can still let me know that you are listening, paying attention, and having a thought without talking."
Me: "We come to school to learn. I know you all have great ideas and comments to share, but we do need to share and take turns. We need to be patient with our friends who need more think time. OK?"
This ended up working so well that I started doing it will all my groups. I eventually found some cute pictures and got rid of my drawing. I added better thought and speech bubbles after I printed them. I laminated these and use dry erase pens to make the line between the arrows.
Guess what? After a few weeks none, I repeat, NONE of my kids blurt out anymore on a regular basis. It is like 99% better. The off time it happens, the children catch themselves, and then raise their hand. :)