The current study estimated the reliability and agreement of student ratings of the classroom environment obtained using the Responsive Environmental Assessment for Classroom Teaching (REACT; Christ, Nelson, & Demers, 2012; Nelson, Demers, & Christ, 2014). Coefficient alpha, class-level reliability, and class agreement indices were evaluated as each index provides important information for different interpretations and uses of student rating scale data. Data for 84 classes across 29 teachers in a suburban middle school were sampled to derive reliability and agreement indices for the REACT subscales across 4 class sizes: 25, 20, 15, and 10. All participating teachers were White and a larger number of 6th-grade classes were included (42%) relative to 7th- (33%) or 8th- (23%) grade classes. Teachers were responsible for a variety of content areas, including language arts (26%), science (26%), math (20%), social studies (19%), communications (6%), and Spanish (3%). Coefficient alpha estimates were generally high across all subscales and class sizes (α = .70–.95); class-mean estimates were greatly impacted by the number of students sampled from each class, with class-level reliability values generally falling below .70 when class size was reduced from 25 to 20. Further, within-class student agreement varied widely across the REACT subscales (mean agreement = .41–.80). Although coefficient alpha and test–retest reliability are commonly reported in research with student rating scales, class-level reliability and agreement are not. The observed differences across coefficient alpha, class-level reliability, and agreement indices provide evidence for evaluating students’ ratings of the class environment according to their intended use (e.g., differentiating between classes, class-level instructional decisions).