This study documents how an urban high school science teacher engaged her English Language Learners (ELLs) in the discourse-intensive science and engineering practices of (1) arguing from evidence and (2) obtaining, evaluating, and communicating information. The teacher taught an introductory integrated science course to classes with a large percentage (44%) of students who spoke Spanish as their first language. We investigated the instructional strategies this teacher used to support her ELLs in the practices of argumentation and communication, and the ways ELLs constructed and communicated claims, evidence, and reasons in whole class and small group settings as a result. From qualitative analyses of teacher interviews, classroom interactions, and student products, we found that the teacher routinely implemented three types of instructional supports to help ELL students argue from evidence and communicate information: primary language support (although she herself was not fluent in Spanish), deliberate scaffolds, and small group instruction. Further, given these multiple opportunities for engagement, we found that ELLs experienced both successes and challenges participating in class, crafting arguments from evidence, and reading and producing written texts: While ELL students constructed aspects of arguments in small groups, the substance of their discussions was not necessarily reflected in their whole class participation or written products. Taken together, our findings emphasize the need to more closely attend to the teaching and learning of discourse in science. We end with ways to strengthen both research on and teaching of science for ELLs.