In a Nutshell: The CLASS is an observational tool for assessing classroom quality in the pre-kindergarten and kindergarten through 3rd grade based on teacher - child interactions in the classroom rather than evaluation of the physical environment or a specific curriculum.The tool is divided into 3 domains: emotional support (positive climate, negative climate, teacher sensitivity, and regard for student perspectives), classroom organization (behavior management, productivity, and instructional learning formats), and instructional support (concept development, quality of feedback, and language modeling). These constructs are rated on a 7-point scale (1-2 low, 3-5 mid, and 6-7 high) recorded in 30-minutes (20 min observation, 10 min scoring) cycles over a period of up to 3 hours (with six as the recommended average number of observation cycles).CLASS is intended to offer the field a reliable, standardized method for assessing classroom quality and the coherence of children's early school experiences. The tool can be used for research, accountability, program evaluation, and professional development.