I understand how frustrating and worrying this must be. But before you rush into medication and treatment, it is vital to understand that ADD does not really concern an inability to pay attention. It's more about attention inconsistency and excess energy.
Both this and selective mutism are complex conditions and need the support of mental health professionals. So here I outline what you should pay attention to when seeking treatment support.
"The hallmark symptoms of attention deficit disorder are easy distractibility, impulsivity and sometimes, but not always, hyperactivity or excess energy," note psychiatrists Edward Hallowell and John Ratey in their book, Driven to Distraction (2011).
Brain disorder specialist Daniel Amen points out there are about seven types of ADD and each responds to different medication and treatments. From my clinical experience, children affected by selective mutism often also have anxious attention deficit disorder or limbic attention deficit disorder.
Both are very different from the classic ADD, and other types of the disorder.