The present study examined the extent to which preschool classroom supports--relational support (RS) and instructional support (IS)--are associated with children's language development and whether these associations vary as a function of children's language ability. The language skills of 360 children within 95 classrooms were assessed using an expressive narrative task in the fall and spring of the preschool year, teachers rated RS in the fall, and observations of IS were collected across the year. Research Findings: Hierarchical linear models revealed main effects of IS, but not RS, on preschoolers' development of expressive language skills. In addition, the associations between RS and IS on children's expressive language development were moderated by children's fall language ability. Specifically, the association between IS and language development was stronger for children with stronger expressive language skills, and the association between RS and language development was stronger for children with weaker expressive language skills. Practice or Policy: These findings suggest that professional development for preschool teachers might focus on aligning classroom supports with the needs of children with weaker language skills who are at risk for difficulty acquiring literacy.