This study sought to explore high school band students' motivation for practicing their instruments using the basic tenets of self-determination theory as a theoretical lens. Exploring levels of self-determination alongside years of musical experience, time reported practicing, grade level, gender, instrument selection, and private lesson study, this study sought to utilize the Music Practice Motivation Scale (MPMS) with a high school instrumental music population. Using multivariate analyses of variance, participants reported higher levels of intrinsic motivational beliefs toward practicing over external motivations. Extrinsically motivated students, however, were more likely to rate stronger agreement with an introjected regulation style indicating the importance of others' views of practice on their own belief system. Despite potential issues with the fulfillment of the psychological need for autonomy, data suggest a weak correlation between private lesson study and the bolstering of intrinsic motivation. Reliability analysis demonstrated strong support for the inclusion of the MPMS in high school-level classrooms when seeking to determine and guide student self-determination to practice. Strong connections were found to support the fulfillment of psychological needs in the instrumental music classroom through targeted activities that focus on the development of intrinsic motivational beliefs focused on feelings of achievement, knowledge, and affect.