The teacher should be in hot water for teaching the 5th amendment incorrectly. From the text of the amendment: "No person shall be... compelled in any criminal case to be a witness against himself..." The 5th amendment gives people the right to refuse to testify, as a witness , in a way that might incriminate oneself. Relatedly, it excludes self-incriminating statements in certain circumstances from evidence in crimi…
I'm not American, but I'm pretty sure the fifth amendment applies to any and all self incriminating statements that can be used to support a criminal charge against you. This is the entire reason police advise you of these exact same rights at the moment of arrest.
By your explanation, anything you say to a police officer or other figure of authority (in this case the school) that leads to criminal prosecution is fair game. That simply isn't the case.
Entire context:
nor shall (a person) be compelled in any criminal case to be a witness against himself, nor be deprived of life, liberty, or property, without due process of law;
Witness is in reference to the general action; not just sitting on a stand.