The adoption of "A Framework for K-12 Science Education" and the Next Generation Science Standards (NGSS) across the U.S. requires that the field of science education develops high-quality instructional materials. This need is particularly urgent as schools and districts are expected to design or adapt instructional materials for an increasingly diverse student population. In this article, we present our conceptual approach for developing yearlong fifth-grade NGSS-aligned instructional materials with a focus on English learners. First, we describe the conceptual framework focused on equity that guided our development work. Second, we describe our design-based research with teachers and our instructional materials development process that leveraged the synergy of the NGSS performance expectations (PEs), phenomena, and students. Specifically, we address equity in our materials in two ways: (a) selection of local phenomena rooted in students' homes and communities and (b) attention to language use in terms of modalities, registers, and interactions. Third, we illustrate our development process using an exemplar unit from our curriculum. Finally, we discuss implications for instructional materials development, including how we productively resolved tensions in developing our materials and how we both benefited from teachers' participation in the development process and promoted their professional learning.