We still don't have a lot of answers. Singing activates the right side of the brain. Our speech center is located on the left side of the brain in most people (including left handed people!). For many stutterers, repetition is intact as well, meaning if you are repeating after someone, you can say it with fluency. There is a condition called Broca's aphasia, but in Broca's repetition is not preserved. Stuttering is currently incurable but I remain optimistic that some day we will have a greater understanding of this condition which will eventually lead to a cure. https://youtu.be/p997-HcSRVY?t=2m31s This video isn't Broca's aphasia, but an example of poor repetition. I think he might have conduction aphasia which means that his comprehension is intact, speech is intact, but the repetition is poor.