Despite substantial attention to measurement and assessment in contemporary education and music education policy and practice, the process of measurement has gone largely undiscussed in music education philosophy. Using the work of physicist and philosopher Karen Barad, in this philosophical inquiry, I investigated the nature of measurement in music education while concurrently exploring the assumptions underlying documents related to the proposed music Model Cornerstone Assessments. First, Barad's concepts of reflection and diffraction reveal the false assumption that measurement captures rather than alters and produces musical experiences. Second, measurement apparatuses are explained as boundary-making practices. Third, the limits of measurement apparatuses are explored through Barad's assertions about experimental inclusions and exclusions and Lyotard's concept of the "differend," and these limits are used to problematize the ambitious, value-laden discourse of documents related to the music Model Cornerstone Assessments. Finally, through Barad's concept of intra-action, measurement is reinterpreted as a process through which "teacher" and "student" emerge. Music education policymakers, teachers, and students might adopt language emphasizing the intra-active nature of measurement and empower themselves to critique and reimagine existing measurement apparatuses and their measurement and assessment practices.