The short answer to your question. Yes, I have failed graduating seniors. The more common problem are seniors in GPA trouble who need an 'A' in my class when they have earned Cs and Ds in the 4 pre-requists. I do everything in my power to help the student learn the material, but ultimately their final grade is a mathematical calculation. I do typically curve my grades at the end of the semester at least 1/2 a letter grade (B+ becomes A-). If the failing grade is still within a percentage point I will move them up to a D- (meaning of hey had at least a 56 to start with), but I never pass someone just because they are a graduating senior. It is extraordinarily rare that a student who has come to class, done the homework, etc. Is in a failing position.