Additional rubrics/measures could include the following:
*Memorization of lyrics: Give them a date by which a piece/section of the piece has to be memorized; have them write out the lyrics.
*Mastery of the music: Have quartets or octets sing the particular piece/section you’ve assigned to be learned by that day. You could designate groups from the get-go (based on proximity) and move quickly from one to the other. “Group three, sing the third verse….” IF you designated preassigned groups, you could also sing an entire song, with various groups “taking over” when you point at them.
The above are especially helpful if the students need more accountability–or if you want to help them take the class more seriously.