An instructional device and associated method for illustrating the positions of keys and their associated notes on a keyboard are provided. The instructional device includes key markers that are adjustably mounted on a support structure in a configuration corresponding to the keys of a keyboard. The key markers correspond in size to the keys of the keyboard and are adjustable between the ends of the group of markers. Indicators are provided on the markers to indicate a chordal relationship between a respective one of the markers and the other markers. Thus, the device can be used, e.g., to indicate the position of the keys on a piano keyboard and, further, to indicate the relationship of the keys and associated notes to one another, such as by identifying various chordal relationships. In addition, the device can be adjusted to thereby illustrate such key positions and note relationships in connection with an inversion of one or more of the key markers relative to the others.