We hold auditions for Advanced Theatre and Advanced Musical Theatre.
For Advanced Theatre (I am the sole teacher)
I meet one on one with students - it's an informal interview during which we discuss the class, the curriculum, the commitment, and their goals. Students then present one monologue of their choosing (approved by me - must be from a published or produced play). I base my rubric upon preparation, commitment (to the class and to the character), and attitude. My Advanced Theatre class is usually quite manageable (between 10 and 16 students), so I rarely turn students away.
For Advanced Musical Theatre (there are three teachers)
Students sing 32 bars (approximately) from a song from a musical. If they wish to sing a song that is not from a musical, they must get permission and justify their choice. They must find a track with accompaniment in the key they want. After they sing, each teacher asks a question or two - an interview. We had hoped to add a dance component to the audition process this year but...The three of us discuss each student - preparation, commitment, and attitude - and are they ready to work at the highest level of musical theatre at our school. This class is usually quite large, so we always turn away more students than we accept.
Hope this helps!