Elementary general music teachers have differing perspectives on the meaning and value of assessment, and few studies have examined how the results of assessment are applied in the classroom. In this case study, I investigated how one elementary general music teacher used information from assessments to individualize instruction. Over the course of seven weeks of observation, think-alouds, interviews, and reading the teacher's journals, I discovered that my guiding questions had implied a simplistic, linear relationship of assessment and differentiation of instruction--that assessment led to individualization. Rather than the direct relationship my questions anticipated, Ms. Stevens' music teaching was more like a tapestry that included nearly omnipresent threads of assessment and individualized instruction--threads that were often so interwoven as to be somewhat indistinguishable. This article describes the reciprocal, spiraling, intertwined nature of individualized assessment, teaching, and learning in Ms. Stevens' classroom. I also discuss the related emergent themes of normalizing independent musicking and structuring open-response activities, which were impacted and undergirded by Ms. Stevens' beliefs regarding the musicality of all children and the purpose of music education.