回复：In this case, what the dean needs to do is to find a solution

Based on your word, dean seems do nothing wrong, except say sorry to your son. If A is your son, and your son is A. Your son (A) lost his binder at school and told you that some one ( other boy) has two same binders. Then what will be your action? And what you expect the dean to do? In any case, you have your feeling and others have their feelings, too. There is no right or wrong in most cases like this. It is a kind of education. You can complain your bad feelings to the dean and ask for an applogize from him. But make sure to discuss with your son and ask his opinion first before you do anything. Othewise you will lose more.