"Scales" (basically a rubric) on the 4-point scale used in the Marzano evaluation system. Rubric includes rhythmic accuracy, note accuracy, steady beat, tone quality, rehearsal and concert etiquette, and posture. I teach 6 classes, 2 orchestra, 2 chorus, 1 guitar, and 1 musical theatre. I created these using some material provided by my county music supervisor (and personal experience), and compiled them to work for any music class so I would not have to create a different one for each class.
Students can also assess themselves through written work, or by simply holding up the number of fingers to describe where they are in their understanding. 3 is supposedly the goal, but I go for a 4!