An unrecognized problem for school children
One of my fellow teachers was having a great deal of trouble understanding her own daughter's bizarre behavior: incessantly garrulous at home, but silent at school. The eventual diagnosis of selective mutism appeared bizarre at first for no one in the district (including the trained psychological experts) seemed to have ever heard of it.
Now with a better understanding of her problem the girl can probably be trained to cope with it and get on with her education, but the identification was key.
It is said that since children eventually do "grow" out of the anxiety disorder that it is not really of any concern. Aside from the fact that it clearly interferes with early schooling, I would counter the argument by pointing out that social interaction is an important--perhaps the most important--learned skill, and failure to master it can lead to a vicious circle of social withdrawal, causing a serious handicap in the adult world.