You and your son have a right to challenge the expulsion at the level of the school, the District or the local Board (sometimes a right to appeal at more than one of these levels of administrative oversight). Time limitations can be short for exercising your right to challenge the expulsion, so act promptly. Get a copy of a description of the process and initiate the appeal immediately. You may want to engage counsel to represent your son in this matter.
It is not uncommon for schools to overreact to these kinds of statements, and it is certainly understandable why they do. But, once the actual level of misconduct has been established and the degree of threat or danger is understood, the school should be willing to de-esclate the matter and impose a more reasonably-scaled penalty, assuming there is a rational basis for believing the accusation that he made such statement(s). Your part, in addition to advocating for a more rationally proportionate penalty, is to make certain that your son understands the depth and nature of the alleged offense, and to make sure that you have adequately explored and dealt with the underlying cause of his improper conduct -- IF he made the statements attributed to him.
My experience leads me to suspect that the school has overreacted here. But such statements by a student -- IF they occurred -- constitute a serious offense and you have to investigate and come to grips with that part of this situation, no matter how improper or excessive the penalty is.
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