Classroom management practices are critical to the success of teachers and students, and a growing number of programs have been developed to improve these practices. However, there has been less investigation into observational tools to assess classroom management and explore whether it can be measured consistently by observers across elementary, middle, and high school classrooms. Moreover, there is a need to determine how classroom management practices vary as a function of school settings and classroom contexts (e.g., class size and racial composition). The current study aimed to examine classroom management practices using the Assessing School Settings: Interactions of Students and Teachers (ASSIST; Rusby, Taylor, & Milchak, 2001), an observational measure administered by trained external observers across 3,263 classrooms. A series of analyses indicated that the ASSIST demonstrated partial MI across contexts, and was particularly robust across class size and racial composition, which enabled us to contrast latent mean differences across developmental levels. Latent means of classroom practices across elementary and middle school were similar, whereas elementary school and high school classrooms differed significantly. The findings provide evidence that the ASSIST is similarly measuring classroom management across classroom contexts but is sensitive to mean differences in classroom management across classroom contexts. [This paper will be published in "School Psychology Review."]