The purposes of this study were to examine (a) whether grade-level differences exist on self-evaluation tendencies over time, (b) if grade-level differences and evaluator differences exist, alone and in combination, on music performance evaluation, (c) if relationships exist between student self-evaluation and expert evaluations of music performance by grade level, and (d) whether differences exist between grade level and music performance subarea (tone, intonation, melody, etc.) on self-evaluation accuracy. Middle ( N=92) and high school ( N=51) instrumentalists participating in two summer music programs self-evaluated their performances during rehearsals, while expert evaluators judged an individual final performance. Results indicated differences between grade levels on performance self-evaluation as the week progressed for some subareas. High school students were more accurate in their self-evaluations than were middle school musicians for all subareas except melody and rhythm. Middle school students' scores showed greater correlation with experts than did those of high school musicians. Both groups were most accurate in their evaluation of melody and least accurate in evaluation of technique/articulation. January 3, 2005 May 11, 2005.