I always go over the grading scale with my students and let them know that class particaption is 10% of their overall grade and a quiz will be 20% of the overall grade and an exam will be 30% and their final exam is 40%, if they do a project it is usually 30% of their overall grade, then at the middle of the course I go over their grades of where they are at that point in the class, so they have an idea where they stand and what they have to do to either keep their grade where it is at or maybe bring their grades up.