My course require students to take 2 mid-term exams and one final exam. What should I do if some students didn't attend the first mid-term exam or the second one. Should I mark them Zero or repeat the exam for them? What is the best strategy in this regard?
Update: Although I gave them instructions from the beginning of the course. Some of them said that they were absent when I gave those instructions. Some of them said that they were sick and some said that they had an appointment with a dentist at same time of the exam, for example!