Computer programs have been developed to assist music educators in three fields: aural training, traditional harmony instruction, and piano teaching. The computerized aid is incorporated in a small computer with graphics capabilities, which features an electronic organ as an input/output device. The computer programs developed for administering aural training. interactively adapt to the weaknesses of individual students. And as a result of a convenient new method for entering the instructional material on the organ keyboard, the instructor and lesson designer are spared the need of learning tedious note-encoding techniques. Other computer programs help assess students' four part harmony exercises, which are entered on the organ keyboard. The printout indicates occurrences of standard harmony "errors", and provides an alternative harmonization based on the student's work, but without the errors. Two new techniques for analysing keys and estimating root pitches are employed: and a context-based analysis of Bach Chorales is described. In an extension to the assessment programs, a system has been developed whereby a melody played on the organ keyboard is interactively harmonized. The voices are chosen according to. standard harmony "rules", Piston's (1949) table of usual root progressions, and musical guidelines. The musician has interactive control over the choice of chords, root pitches and pass ing notes. Slowed-down playback by the computer programs, together with a special visual display of the music (both developed by Tucker, 1977) are used to reveal details of piano playing beyond the scope of existing aids. As with the Aural Training and Harmony Assessment systems, examples are given of t.he computer's application in a teaching situation. The thesis concludes by describing a concert pianist's reactions to the computer's revelations about his playing.