The purpose of this study was to evaluate the psychometric quality (i.e., validity and reliability) of a rating scale to assess pre-service teachers' lesson plan development in the context of secondary-level music performance classrooms. The research questions that guided this study include: (1) What items demonstrate acceptable model fit for the construct of lesson plan development in the context of a secondary-level music performance classroom? (2) How does the structure of the rating scale vary across items? and (3) Does differential severity emerge for academic administrators or music education content specialists across items? Using multiple teacher effectiveness frameworks, the lesson plans in this study were evaluated using a 4-point Likert-type rating scale (e.g., "strongly agree," "agree," "disagree," "strongly disagree") consisting of five domains: (a) instructional planning, (b) instructional delivery, (c) differentiated instruction, (d) assessment uses, and (e) assessment strategies. Secondary-level school administrators (n = 8) and music education content specialists (n = 8) rated 32 lesson plans using a balanced incomplete assessment network. The multifaceted Rasch measurement partial credit model was used in this study. Results suggest higher rater severity among administrators than music specialists. Of the 68 potential pairwise interactions examined in the study, 5 (7.4 %) of those were found to be statistically significant, which indicates that 5 raters demonstrated differential severity across at least one lesson plan. Implications for student teacher preparation, teacher effectiveness, and the validity of measures are discussed.