This article explores the special case of integrative teaching and learning in music as a model for 21st century music education policy reform based on the principles that have evolved out of arts integration research and practices over the past century and informed by the recent rising tide of evidence of music's impact on brain capacity and cognitive skill development. Rather than taking sides in a contentious and unproductive debate between the value of music education for its own sake versus support for music integration as a means for enhancing learning in other disciplines, the authors believe that the Music Plus Music Integration (M+MI) framework now resolves this false dilemma that has limited the evolution of music education school policy over the past two decades. Examples of curricular frameworks, teaching practices, and research findings from several research-based Music and Arts Plus Arts Integration initiatives in elementary and middle schools make clear the ways in which the underlying principle of "differentiation" and "synthesis" serves as an effective strategy for optimizing learning in artistic and academic domains and also benefits the entire 21st century school community in and through the study of music.