Oh that is terrible! Yes, absolutely call the school. Also, I'm worried about your son's welfare. Taking a knife and saying that he is going to kill himself . . . was it dramatics/theatrics or was he THAT upset? Suicide ideation . . . a plan on how you would kill yourself is real and people are typically depresse that exhibit this. Suicide always comes out of depression. With young people---- they are more spontaneous and more typically willing ot act on impulse. If you feel he really is considering something like suicide, call your doctor and tell them this right away. They'll begin treatment immediately for him. good luck
PS: again, unacceptable behavior by kids at school. call school officials and let them know as soon as possible.
You should contact the principal of the school this is not acceptable and in fact is bullying .Speak firmly with the school, also his teachers should be stopping this kind of extreme behavior..Can you do home schooling where you live, as if it continues it may be an option.Good Luck I am sorry your son has had this ignorance put on him...Let us know how he is doing ...