Dual language learners (DLLs) - children who are learning and developing two languages - are among the fastest growing groups of young children in the United States and currently compose a third of the public preschool population. Although evidence suggests that preschool education is beneficial for DLLs, little is known about which instructional supports in the preschool classroom best promote DLLs’ early learning skills. Drawing on a newly-collected sample of Spanish-speaking DLLs in an English-dominant, mixed-delivery public preschool system for children in low-income families (Head Start; school-based pre-k), this paper focuses on two instructional dimensions of the preschool classroom expected to support DLLs’ learning: supports for home language and supports for English acquisition. We test for associations between these classroom supports and DLLs’ English language skills, quantitative reasoning skills assessed in English, and home language skills at the end of the preschool year, and whether any such associations are moderated by the proportion of DLLs in the classroom. Controlling for baseline skills, results indicate positive associations between classroom supports for home language and quantitative reasoning skills and Spanish expressive vocabulary skills at the end of preschool. Associations varied by proportion of DLLs in the classroom. Supports for English acquisition did not predict any outcomes. This study adds to an emerging body of research suggesting classroom instructional supports for DLLs’ home language may be important not just for the maintenance of children's home language, but also for the acquisition of foundational pre-math skills. Additionally, findings suggest support for home language is possible even in preschool classrooms where the teacher does not speak the home language. The DLL composition of the classroom also warrants attention as a moderator of these associations. (author abstract)