From “The Encyclopedia of Children’s Health” (bold italics emphasis mine):
Mutism is a rare childhood condition characterized by a consistent failure to speak in situations where talking is expected.
In mutism, the child has the ability to converse normally and does so, for example, in the home, but consistently fails to speak in specific situations such as at school or with strangers. The condition is also called selective mutism, to differentiate it from children who are physically unable to speak. Experts believe that this selective problem is associated with anxiety and fear in social situations such as in school or in the company of adults. It is, therefore, often considered a type of social phobia. This is not a communication disorder because the affected children can converse normally in some situations. It is not a developmental disorder because their ability to talk, when they choose to do so, is appropriate for their age level. This problem has been linked to anxiety, and one of the major ways in which both children and adults attempt to cope with anxiety is by avoiding whatever provokes the anxiety.
Mutism is believed to arise from anxiety experienced in social situations where the child may be called upon to speak. Refusing to speak or speaking in a whisper spares the child from the possible humiliation or embarrassment of saying the “wrong” thing.
Read more on Mutism: http://www.healthofchildren.com/M/Mutism.html#ixzz2UAFnhlN2
Mutism is a great example of Mind-Shame. Like other examples of unhealthy/ toxic learning, including ‘math anxiety‘ and ‘reading shame‘, mutism develops from and extends emotionally maladapted learning.