This mixed-method study examines the relationship between classroom discussion and student performance in twenty 3rd and 4th grade classrooms in northern California with 50% English language learners (ELLs). Discussions were scored on features including use of multiple approaches for solving problems, students' opportunities to speak, equitable participation, explanations, and connections between ideas. A linguistically-modified math assessment measured student performance. Quantitative analysis using hierarchical linear modeling (HLM) showed that the discussion features "variety of approaches" and "equitable participation" significantly contributed to the explanation of between-class variation in assessment scores, above and beyond that explained by prior mathematics performance and English proficiency. Importantly, mathematical discussion was equally beneficial for students classified as ELLs and those not classified as ELLs. Two classroom vignettes illustrate the different features of discussion and offer insight into ways ELLs contributed to the discussion in different contexts.