Stammering is not a neuropsychiatric disorder, but a disorder of impulse transmission from the brain to the speech apparatus.
Stammering needs to be treated with speech exercises, but from personal experience with my own child, I can successfully approach it using:

• vitamins and amino acids
• nootropics
• nutritional corrections
• Tai Chi exercises
• physical training
• relaxation and meditation methods and visualisation

Recovery of stuttering can be achieved by stimulating the neuroplastic mechanisms of the development of the underdeveloped nuclei of the brain.