Chords are formed and harmonics are formed. To be pleasing to the ear, notes must be combined in a prescribed manner and progression. All of this is very specifically spelled out in music composition text books. If each note were to be translated to a number, one would find a splendid array of mathematical formulas and progressions at work in music. Learning to play an instrument involves an intricate interaction between the right and left sides of the brain.
Music helps in the coordination of hands, eyes, ears and creative emotion combined in one exercise.
Recent research is confirming some learning takes place for reasons other than just the value of the specific information being learned. This research confirms there is value in some learning exercises because they trigger certain important connections in the growing brain. In other words, the type of stimulus a child gets at various stages of this development actually impacts the way in which the brain physically grows. Research has shown music in education can increase the level of spatial temporal reasoning in students. Also check out Non-musical Outcomes of Music Education which summarizes information from Dr. James Hanshumaker as presented in the Bulletin of the Council of Research in Music Education.