A master class is generally taught by a recognized performer or music educator in connection with a visit to the area for some other purpose. The insights that these individuals can offer about performance, technique, and music in general can be invaluable, because the master is teaching from long experience of making music at a professional level. Most such master classes will involve piano students of all ages, although usually the more advanced students in a given age group will perform simply because they are in the best position to learn the most. However, such classes are often so stimulating that anyone with an interest in learning to play better can benefit enormously from just sitting in the audience. For this reason, you should try to attend master classes even if you are not playing yourself. Attendance at the class is usually free, although there is often a nominal charge for those actually performing for the master.
At a typical master class, the students perform from memory the music that they have prepared. The master teacher usually listens either on stage or seated in the audience following the score (music) while the student performs. It is customary after the student performs and before the teacher begins to work that the student takes a bow. After the student performs, the master teacher will either stand by the student or be at another piano and start to work with the student, basically giving them a lesson on the music while in front of an audience. Often the master teacher will ask questions about the music, and the student should be able to verbally communicate to the teacher. The master teacher has his/her choice of things to work with the student, perhaps technical suggestions, perhaps interpretive ideas. The teacher will most certainly always have the student play certain parts of the composition again, trying to incorporate the new ideas or suggestions. The student is expected to try to the best of their ability to digest and perform the music using the new ideas or suggestions. It is urged not to argue with the master teacher; as that is courting death! In the overwhelming majority of cases, the master will be gentle in offering constructive criticism and effusive in praise, so the experience of participating in a master class is not something to be feared but eagerly anticipated. We might not always agree with the master teacher, but getting another perspective and opinion of a work of music is always worth it. It is a good idea for the student to know all the written terminology in the music, as well as the key the music is in, as well as some biographical information about the composer and his music. This way, if the master teacher should ask questions about these subjects the student is prepared to answer the questions intelligently and coherently.
It is good protocol that, after the master class is finished, the performing student shake the hand of the master teacher and verbally express thanks and appreciation for the time spent. If the class is free for participants, chances are that the organization sponsoring the class has paid the teacher's fee. In that case, it is a good idea to thank the sponsor in writing so as to encourage more such classes.