This study's purposes were to develop a rating scale for midlevel band performance and validate a theoretical structure for the scale. Research questions were (a) What qualities describe excellent seventh- and eighth-grade band performance? (b) What items constitute a Midlevel Band Performance Rating Scale (MBPRS)? (c) How reliable is the MBPRS? and (d) Does the MBPRS demonstrate construct validity? Mixed methods were employed, in particular the exploratory sequential design, which has a three-phase variant involving the development of an instrument of assessment. During Phase 1, 20 middle school band directors were asked to provide descriptions of excellent band performance at the middle level, of whom 10 responded. Their statements were grouped into categories and translated into 27 items appropriate for a rating scale. During Phase 2, 151 students participating in four different concert band ensembles at three universities used the items to rate one seventh- and one eighth-grade band performance. After item analyses confirmed their suitability, the 27 items became a Midlevel Band Performance Rating Scale. Internal consistency (coefficient alpha) of the 27 items was good for both sets of ratings, .90 for seventh grade and .92 for eighth grade. Phase 3 established construct validity for the two sets of ratings by confirming that their underlying structures were consistent with previous research.