This is one of the most common student responses; because students are so accustom to judging their learning and their merit based on the A-B-C grading rubric, students often feel lost and disconnected at not knowing their grades on each assignment.

Besides the newness of this model (of evaluation), there is really no problem. I usually explain to my students (who often come up next with, 'how do I know what to work on?') that they should be working hard on all of their assignments and working to learn. Therefore, the number or letter grade is of no consequence. With reassurance that I write comments and help them, students usually accept this model (especially after their first assignment is "returned" with comments).