Every year, I have insisted on having my students reflect on their musicianship. In my first year of teaching, I started with Post-Concert Reflections: having them write what went well, what can be improved, and their overall feelings in regards to the recent performance. After 10 years of teaching, it now has many layers.
At any moment during class, I can teach students to reflect. We play an exercise out of the method book. I ask the students to think of one compliment and one critique for themselves, their section, or the entire group. Depending on time, I ask for them to share ("I would like 4 compliments and 4 critiques"). Then we play the exercise again with them applying what they just shared. Sometimes the results are amazing!
I have also create Progress Portfolios where the students set goals and then monitor their progress over multiple classes and/or weeks. Depending on the age and level of the group, these can be simple goals ("I will use proper posture every time I play") to more complex ("I will improve my intonation by adjusting breath support and embouchure").
After every performance, every student completes a reflection. We reflect on individual accomplishment and group accomplishment. If judging and comments were involved with the performance, I ask the students to reflect on which comment "stuck" with them the most and which suggestion they could immediately implement.
I sent a proposal to the State Conference planning committee and I hope to be selected to present a session on Student Reflection in the Performance-based classroom. I just have to wait and see :)