What you do in the hour after a bad grade, door shut, nobody watching, is a better report card on you.

A grade measures one piece of work on one day. The hour after it measures something longer lasting: whether you look at what went wrong, whether you take it out on somebody, whether you quit quietly and call it not caring. Nobody grades that hour, which is exactly why it is honest.

Decide in advance what that hour should look like, since you will not be in a state to decide it then. Something like twenty minutes of being annoyed, then one look at what you actually got wrong. A plan keeps a bad afternoon from becoming a bad term.