"Lastly, as long as his scholars were under his musical direction, he did not allow them to study or become acquainted (besides-his own compositions) with any but classical works. The understanding, by which alone what is really good is apprehended, develops itself later than the feeling, not to mention that even this may be misled and spoiled by being frequently engaged on inferior productions of art. The best method of instructing youth, therefore, is to accustom them to what is excellent. The right understanding of it follows in time, and can then still farther confirm their attachment to none but genuine works of art." From The Musical World, describing J.S. Bach's teaching methods.
Also see my earlier post Educational Aesthetics