While most piano students want to learn how to read music, the teacher should always include the teaching of musical theory. Without explaining that harmony isn’t "random", but has guiding principles, for instance, students will begin connect more deeply to songs they play. If we simply instruct students only how to reproduce melody, chords, and rhythm without explaining what function say, a "tonic", "subdominant", or "dominant" chord might have in any song, we haven’t done our job. Music students need to understand how harmonic progressions are guided by the principle of "stable" and "unstable" chords. When they are able to identify the I, IV, and V chord of all 12 major keys, they will begin to understand tonality better, see patterns, and notice repeating chord progressions in the songs they like. The tonic, or I chord is a chord of repose, and is considered "most stable" . The subdominant or (IV chord) is less stable. The dominant chord (V chord) is most unstable and typically wants to progress to the tonic (I major). Most songs kids like use these chords: I, IV, and V. These are considered the "primary chords" in any key. It is helpful to let them know this so that you can demystify the music they listen to and help them have a better grasp as to what they are hearing.