How do teachers determine a grade for a subject?

I know so far it includes class participation, homework, and your tests. I got a bad grade on the only test on a subject -- almost right when the quarter is about to end! I have done all work and everything, which would give hundreds, just the test as the problem. What do they do each day? If you do not do the subject on that certain day, will they still count the participation, ex.? What am I missing, is the subject grade in for an A, and how to maybe get it up?