A marked difference in the conduct of vocal instruction may be noted here between the old and the new system. Most teachers follow the custom nowadays of giving strictly private lessons; they allow nobody in the studio but the student who is actually receiving a lesson, in addition of course to the accompanist and an occasional visitor. The old masters always preferred to teach in small classes. Four, five, or six pupils would form a class. Each one would receive his lesson in turn, the others listening and profiting by the instructor’s criticisms and suggestions.
In addition to its other advantages, this system was admirably adapted to further the ear training of the students. Week by week each pupil could observe the progress of his classmates, and could thus become acquainted with all the fine shades of difference in tone quality which a voice exhibits in the course of cultivation. By the time a student had finished his course of instruction, his ear would be familiar enough with every aspect of vocal tone to fit him, if he desired, to make a beginning in the training of voices himself.
Taylor, David Clark. “New Light on the Old Italian Method: An Outline of the Historical System of Voice Culture, with a Plea for Its Revival.” (1916).