Background: Research has documented the importance of high-quality early childhood experiences in preparing children for school. Quality rating and improvement systems (QRIS) have recently emerged in many states as a way to build quality of child care and to promote better child outcomes. Objective: The goal of this study was to determine if preschool classrooms representing various levels of QRIS structure and status differ on classroom process quality as assessed by several observational tools (i.e., the Early Childhood Environmental Rating Scale-Revised, the Classroom Assessment Scoring System, and the Early Language and Literacy Observation Tool). Methods: We randomly selected 103 teachers in 96 classrooms from 48 full-time child-care programs, and compared classroom quality in QRIS participating programs with classrooms in non-participating programs, and classroom quality across QRIS rating levels. Results: From multilevel analyses, we found that teachers in QRIS participating programs scored higher on global quality of classrooms, emotional support, instructional support, and literacy environment than those who were in non-participating programs after controlling for center-level and classroom-level variables. Teachers in the highest rated QRIS programs exhibited better process quality, including emotional support, classroom organization, instructional support, literacy environment, general classroom environments, and language curriculum than those in lower level programs. Conclusions: This study suggests that QRIS may be a promising investment for quality in early childhood education and care, which is a reasonable proxy for improving children's school readiness.