Orthogonal to the music theory itself, there's the question of general learning methodology.
One approach that seems promising is combining spaced repetition with knowledge graphs. The graph helps map knowledge areas and dependencies. For instance:
- Notes depend on Pitch.
- Intervals depend on Notes.
- Chords depend on Intervals.
...etc. The system would ensure concepts are mastered in the right order before progressing and use spaced repetition [1] to determine the optimal intervals for quizzing the student.
A site discussed on HN previously outlines how it applies this approach to teaching math [2].
Also, check out Hookpad [3], which offers some innovative tools for learning music theory.
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1: https://en.wikipedia.org/wiki/Spaced_repetition