Research Findings: Children's oral language skills lay the foundation for later literacy and can be fostered through responsive conversations with teachers. However, such conversations are rare in preschool, particularly between teachers and dual language learners (DLLs), or students who speak a minoritized language at home. DLLs benefit when their home language is used and instruction is provided in small groups, but few studies have explored the degree to which preschool teachers "code-switch," or alternate between languages within a single group context. This study draws on 10 transcribed video-recorded observations of Head Start preschool classrooms to describe five teachers' flexible use of Spanish and English with their Spanish-English DLL students across whole and small group contexts. DLL students' language use was examined to explore the role of group context and teacher code-switching in fostering DLLs' participation in classroom conversations. While relative Spanish use varied widely, all teachers code-switched more frequently in small group than in whole group. The 25 DLL students spoke more, took longer turns, and used more Spanish in small group versus in whole group. Practice or Policy: Our results suggest that teacher code-switching and small group instruction create contexts that are conducive to DLLs' participation in classroom conversations. [This is the online first version of an article published in "Early Education and Development."]