Modern-day teaching theories are all well and good. Well, at least some of them are. There's a lot of poppycock and snake oil out there masquerading as teaching advice, most of it written in polysyllabic gobbledegook and bristling with phrases like curricular assessment outcomes and broad-spectrum syllabic strategies and the like. Even after tossing all of that pedagogic flapdoodle into the dumpster where it belongs, good ideas remain. Nonetheless, they're the icing on the cake, the cream in the coffee, the sprinkles on the ice cream cone, [your preferred culinary metaphor here]. Teaching is teaching is teaching. It's been around for a long time.
There's really no substitute for the experience of the past, if for no other reason but that there's a lot more past out there than present. Folks have been training their offspring for a very long time and only the most callous modernist would assume that nobody made a decent job of it. While certain aspects of old-time pedagogy are best left behind—I vote to nix starvation, neglect, and physical abuse—we teachers have a great deal to learn by asking how our predecessors did it. That may mean nothing more complicated than conjuring up memories of our own teachers who have left a particularly good impression, or those teachers who have wound up wearing the Cone of Shame for their remembered offenses or shortcomings.
Clearly some disciplines are best transmitted via one-on-one, mentorship/apprenticeship style, while others work better in a large group context, with one teacher passing on ideas to a sizeable group of people. It's hard to imagine anybody becoming a competent violinist without a teacher right there, guiding and cajoling and supervising and criticizing and inspiring. You can't learn to play the fiddle out of a book, any more than you can learn to dance or ride a bicycle or become an expert bowler. That's all teaching by mentorship.
At the same time there's not much point to teaching history one-on-one. Such subjects lend themselves well to lectures, classrooms, presentations and exams and term papers. It's teaching by broadcast. That doesn't make it easier or better or worse than the other; it's just different. There are plenty of mentor-type teachers who would be lost at sea, and ineffectual, standing before a note-taking class in a lecture hall. Ditto the opposite: a teacher who shines in the lecture hall might feel trapped, claustrophobic, or nearly paralyzed in a one-on-one situation.
Not often acknowledged but nonetheless real is a point about halfway between the two—a small-group dynamic that requires a teacher to balance between the exclusive style of mentor-style teaching and the breadth of classroom lecturing. The number of disciplines in question is small, and thus doesn't get much attention from the teaching corps.
Many of these disciplines fall under the general heading of "lab" type courses, those which impart a certain amount of empirical information but are largely experiential and require some personal supervision. Thus it shouldn't be surprising that they tend to cluster in the sciences and in the arts. In music, that means the courses in eartraining & solfege and those in music theory.
There's an ancient wisdom in the way that most conservatories wrap eartraining and theory courses under a single banner. Many solfege teachers are also theory folks, and many come to the field with backgrounds in either performance or composition; solfege teachers who began as music historians or musicologists are fairly rare. Both theory and eartraining are by and large experiential and performance-oriented disciplines.
That might seem obvious enough regarding solfège but less so as to music theory. However, music theory has very little to do with the absorption of facts or philosophies or empirical data, although certainly some such is involved. Mostly music theory is a matter of doing, just as is the case with solfège or violin playing or bowling. Students of music theory can learn most of the basics from brief handouts, but applying those ideas to real, living and breathing music is something else entirely. For music theory to be anything other than vague notions contemplated from one's armchair, pencils need to be gotten out, music paper written all over, mistakes made, music misinterpreted, progressions and counterpoint exercises written, analyses conceived and presented and defended.
So it is that conservatories since the earliest days have recognized that the small class is the idea forum for both eartraining and theory. I generally work with 12 to 15 students in those classes; some teachers might prefer a smaller group, but I'm comfortable with the dozen-ish. That makes for enough students to provide an ensemble for choral singing and sight-reading practice, while at the same time allowing me at least a little time for some one-on-one attention during class. Studio-type lesson teaching would work poorly for eartraining; students need to hear other people, to compare themselves with their betters or inferiors and to feel the heat of competition, not to mention the possibility of being publicly embarrassed by a poorly-prepared in-class performance. A theory class offers a similar dynamic, although the emphasis moves a bit to the front of the class and the teacher at the whiteboard. At the same time, the students will be called upon to answer questions, to work together on progressions or formal analysis or whatnot, and to deal with the same issues of competition and inspiration as in any other class.
To that end, my department and I have worked out a core curriculum in which our students not only take their theory and eartraining in small classes, but they have the same teacher for both disciplines, and stay together for four full semesters. All in all it's a single comprehensive course that we have split into two classes to accomodate those students who might be notably stronger in one of the two disciplines and therefore need appropriate placement. Those students make up only a small percentage of the whole, however; most journey through the two years together.
Thus I spend my days teaching in a manner that would be completely familiar to my predecessors in Leipzig or Paris or Naples. Although some of the materials have changed—we do a lot of Bach nowadays, whereas back in the Neapolitan Poveri del Jesu they would have done a lot of Durante—the overall technique, the gestalt, remains the same. It doesn't need any modern educationese-laden screeds and syllabi and curricula. We already know how to do it just fine, and we've known for centuries and centuries. If it ain't broke, don't fix it: sometimes learning is best served by sticking with the tried, the true, the known, and the proven.