Research Findings: The present study investigates both the proximal processes and contextual influences on children's oral language development in preschool. We examine whether teacher language practices vary across activity settings and program type, which teacher language practices predict children's oral language skills, and potential differences in children's language learning trajectories. The instructional time in a diverse sample of 15 preschool classrooms was recorded and coded for teacher language practices hypothesized to support children's language development, including conceptual and interactive talk. Children (n = 99) were assessed at the beginning and end of the school year with a comprehensive measure of oral language development. Results indicated that there was substantial variation across activity settings and program type, with more beneficial language practices used more often in large group settings and in preschools with extensive professional development and coaching support. The specific teacher language practices of vocabulary talk and elicitation practices were positively related to children's language, controlling for pretest scores, child age, and program type. Practice or Policy: Findings indicate several leverage points for intervention, such as balancing time spent in different activity settings, maximizing the potential of small group time through elicitation strategies, and building in additional supports for interactive language during centers time.