The purpose of the present study is to examine associations between quality of teacher-child relationships from preschool through third grade and children's third-grade achievement using Phases I, II, and III data from the National Institute of Child Health and Human Development Study of Early Care and Education, a prospective study of 1,364 children from birth through sixth grade. There are three main findings. First, positive associations were found between quality of teacher-child relationships and achievement. Second, high quality teacher-child relationships buffered children from the negative effects of insecure or other maternal attachment on achievement. Third, the effect of quality of teacher-child relationships on achievement was mediated through child and teacher behaviors in the classroom. In sum, high quality teacher-child relationships fostered children's achievement. Implications for educational practice are discussed. (Contains 5 tables and 2 figures.)