Music making requires many kinds of habits of mind—broad thinking dispositions potentially useful outside of the music room. Teaching for habits of mind is prevalent in both general and other areas of arts education. This chapter reports a preliminary analysis of the habits of mind that were systematically observed and thematically coded in twenty-four rehearsals of six public high school music ensembles: band, choir, and orchestra. Preliminary results reveal evidence of eight habits of mind being taught: engage and persist, evaluate, express, imagine, listen, notice, participate in community, and set goals and be prepared. However, two habits of mind that the researchers expected to find taught were not observed: appreciate ambiguity and use creativity. These two nonobserved habits are ones that arts advocates and theorists assume are central to arts education. The chapter discusses how authentic assessment of habits of mind in the music classroom may require novel methods, including the development of classroom environments that foster additional levels of student agency.