So I require my American government students to take three exams over the course of the semester, and then, if they wish, they can take an optional final. (I only count the optional final if it helps their grade.)
Notably, the optional final DOES NOT substitute for one of the three required exams. You can’t drop a lowest score, or skip an exam and take the final in its place.
I try to make this abundantly clear on my syllabus and in repeated in-class announcements. To wit:
NOTE: THE FIRST THREE EXAMS MUST BE TAKEN. THE SCORES YOU RECEIVE WILL COUNT IN YOUR FINAL GRADE, WHETHER YOU TAKE THE OPTIONAL FINAL OR NOT. THE OPTIONAL FINAL DOES NOT SUBSTITUTE FOR ONE OF THE THREE MANDATORY EXAMS.
So why in the world did so many people skip the third exam BUT TAKE THE OPTIONAL FINAL ANYWAY???????????