Research on teacher-child relationships, classroom environments, and teaching practices provided the rationale for constructing a system for observing and assessing emotional and instructional elements of quality in early childhood educational environments: the Classroom Assessment Scoring System (CLASS). The CLASS provides a framework for observing key dimensions of classroom processes, such as emotional and instructional support, that contribute to quality of the classroom setting from preschool through third grade. This article provides information about the development, field testing, and use of this instrument in prekindergarten. Data from a national sample of 224 prekindergarten classrooms in 6 states are presented to provide reliability and validity information. The full range of the scale was used for the majority of ratings. Ratings reflected generally positive impressions of the classroom environment and teacher-child interactions. Factor scores from the CLASS were related to the Early Childhood Environmental Rating Scale (ECERS) total score and most strongly related to the ECERS interactions and language-reasoning subscales. Implications for policy and professional development from prekindergarten to third grade are discussed.