The purpose of this study was to develop and test the construct validity and reliability of a self-report measure of self-regulated practice behaviors for beginning and intermediate instrumentalists. A questionnaire was designed to assess the motive, method, behavior, time management, and social influences dimensions of the theoretical model of self-regulation proposed by McPherson and Zimmerman. The questionnaire's construct validity was tested using confirmatory factor analysis, and a preliminary assessment of predictive validity was estimated by correlating the measure with self-reported practice habits. The measure's reliability in regard to internal consistency and consistency over time was assessed as well. The sample consisted of middle school band students in grades 6 to 8 (N = 302). Confirmatory factor analyses indicated that a model including factors representing the dimensions self-efficacy, method/behavior combined, time management, and social influences was the best fit. Cronbach's alpha and test-retest reliability results indicated good to excellent consistency across all self-regulation subscales, with coefficients ranging from 0.76 to 0.90. Significant correlations (p less than 0.001) between the self-regulation subscales and self-reported practice habits (i.e., time spent practicing, average daily practice efficiency, percentage of time spent on formal practice) provided preliminary evidence of predictive validity of the measure. (Contains 3 tables.)