In the DISCUSS (Dialogic Inquiry for Socioscientific and Conceptual Understanding in School Science) research project, a Socioscientific Issues (SSI)-based curriculum is developed and implemented in sixth-grade science classrooms with predominantly English language learners (ELLs) in Houston, Texas. A four-week space unit is designed in collaboration with researchers and science teachers to improve students' science content knowledge, reasoning and argumentation, and academic language through dialogic inquiry of a central question: "Should the U.S. government increase or decrease funding for space exploration?" The unique features of the curriculum include the expansion of 5E instructional model to the 7E model for ELLs, the use of classroom discussions to facilitate reasoning and argumentation, and the integration of effective literacy strategies in lessons. Students investigate four-domain issues--technology, environment, economy, and public policy--associated with space exploration by reading argument texts, engaging in teacher-led whole class discussions and peer-led small-group discussions, and hands-on group work. At the end of the unit, students write an individual decision letter to address the central question. The multidisciplinary DISCUSS curriculum is promising to help teachers create language-rich science classrooms and promote science learning, reasoning and argumentation, and academic language development of all students especially ELLs.