The present study examines the extent to which the association between school readiness skills and preschool classroom quality is higher in classrooms in which quality is above a threshold than when quality is below that threshold. A sample of 222 teachers and 875 children participated in a large, multi site study. Classroom quality was defined as effective teacher-child interactions and measured by the Classroom Assessment Scoring System. Children's language, literacy, and inhibitory control were assessed in the fall and spring. Using predetermined thresholds for high quality, associations between quality and children's skills in inhibitory control and phonological awareness were greater when CLASS Emotional Support was rated higher, while associations between quality and skills in literacy (phonological awareness and print knowledge) were greater in classrooms in which CLASS Classroom Organization scores were higher. Effect sizes were moderate to large (d = 0.43-0.84) for associations between outcomes and quality in the higher quality ranges. Empirical approaches to identify thresholds, indicated relations between inhibitory control and both Classroom Organization and Emotional Support as higher when teacher-child interactions were rated as more effective. These results contribute to emerging evidence that features of classroom experience, such as qualities of teacher-child interactions, are more strongly associated with higher levels of children's school readiness skills when the nature of those experiences (i.e., interactions) are in the upper ranges of the distribution. However, the evidence reported herein do not warrant recommendations for specific thresholds and inconsistencies in the study's findings in comparison to previous research require further investigation before direct implications for thresholds in quality would be warranted. (C) 2015 Elsevier Inc. All rights reserved.