This study focused on two fourth-grade science classrooms with English learners (ELs), exploring how teachers supported students' science and language/literacy learning in different language contexts. Three a priori research-based practices recommended for supporting science learning framed our exploration: (a) negotiation, opportunities for individual and social construction and critique of knowledge; (b) embedded language, opportunities for language and literacy learning as a natural aspect of science; and (c) nonthreatening learning environments, opportunities for social apprenticeship and interaction. We provide insights into how science instructional practices supported ELs' science and language learning. One key implication is that enacting these three principles of practice in students' first language (Spanish), when less linguistic scaffolding is required, creates more opportunities to focus on disciplinary content and exploration of students' ideas. The second key implication is that using open-ended questions and extending prompts and questions through exploration-based lessons was an effective way to support and guide ELs (and all students) to rich understandings of key concepts. A third key implication is that although teachers delivered instruction in two different languages, when they enacted these principles, they fostered student engagement and interest in science. Effective implementation of these practices outweighed the language of delivery.