The associations between trajectories of child care quality from ages 2 to 4 years and children's cognitive performance at 4 years (= 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] = .39, confidence interval [CI] = .21–.66), receptive vocabulary (ES = .41, CI = .14–.68), and school readiness (ES = .32, CI = .06–.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.