The associations between trajectories of child care quality from ages 2 to 4 years and children's cognitive performance at 4 years ("n" = 250) were tested. Distinct quality trajectories were identified: low and high ascending Teaching and Interactions trajectory; low and high Provision for Learning trajectory. Membership in the high ascending Teaching and Interactions trajectory was associated with better numeracy (effect size [ES] = 0.39, confidence interval [CI] = 0.21 - 0.66), receptive vocabulary (ES = 0.41, CI = 0.14 - 0.68), and school readiness (ES = 0.32, CI = 0.06 - 0.58). The results suggest that a pattern of increasing quality of teacher-child interactions during the preschool years, particularly with regard to supporting the development of language, has a moderate impact on children's cognitive development. (Contains 5 tables and 1 figure.)