Class participation grades

Grades are based on applying the following schema to each student's participation in each class and then averaging across all classes (excluding the introductory 1st class).

5:        Absent (up to a maximum of 4 times)
6:        Present but silent
7:        2 or more ordinary contributions
8:        1 good contribution (that I consider particularly pertinent, thoughtful, and sophisticated)
8.5:     2 good contributions (or one 'excellent' contribution, which counts double throughout)
9:        3 good contributions
9.5:     4 good contributions
10:      5 good contributions
11:      7 or more good contributions

Obviously final grades cannot be above 10, but 10 is possible.