Abstract: This invention is a music theory teaching aid which structurally includes a base member, a main wheel member pivotally attached to the base member at a central location, and twelve secondary wheel members each pivotally attached to the base member at circumferentially spaced-apart points, radially outwardly from the main wheel member. The base member bears indicia indicating major scale reference notes for each of the twelve musical keys. Each reference note is associated with one of the secondary wheel members. The main wheel member is pivotable to selectively align indicia thereon to correspond with major reference notes on the base member such that the order of diatonic notes of a selected key are indicated for each mode of the selected key. Indicia on each secondary wheel member radially divides it into twelve equal sections representing chromatic steps of an octave.