Good teachers let their students know how they will be graded and report card marks are not surprises to their students.
I'm not a good teacher. My ninth period students expect grades of 90 when their highest test grade all semester has been a 65. I have a student who doesn't understand why he cannot pass in spite of the fact he hasn't opened a notebook since day one and he has never done more than put his name on an exam. The boy who comes and stares off into space but managed to get a 67 on one exam also feels he should be passing. Some of my college students are just as bad. They don't do homework, fail exams, come to class late and leave early but need the class to graduate and they expect to pass.
If my grading rubric was 40% attendance, 40% socialization with friends, 10% playing with a cell phone, and 10% everything else, I would understand their shock at not making it. I don't think that is what I told them I expected them to do, but I guess I am wrong.
I'm not a very good teacher.