Public speaking classes are particularly difficult for several reasons. When I grade your speaking you perceive that I am grading you as a person. Consequently a low grade on a speech is often more difficult to accept than a low grade on a physics exam. Sometimes anxiety prevents students from demonstrating their full ability. Sometimes it is hard to separate elements of content and delivery.
Speeches are difficult to grade because of their ephemeral nature.
As speech critics we accept that we cannot see and hear everything that happens in a speech event. That is one of the reasons we use videotapes. I use a criterion-referenced grading system. What that means is that I will evaluate you on the basis of pre-established criteria that I will try to explain to you in detail. Grades are earned , not given, as in a gift.