Within the school library community, there have been persuasive calls for school librarians to contribute to science learning. We present a conceptual framework that links national standards of science education (Framework for K–12 Science Education: Practices, Crosscutting Concepts, and Core Ideas, referred to as “Framework”) to core elements embedded in AASL’s Standards for the 21st-Century Learner (referred to as “Standards”), the standard that guides the teaching and learning of multiple literacies for which librarians are responsible in schools. Based on this conceptual framework, we highlight how four middle school librarians in a large school district in the mid-Atlantic region of the United States enact and expand their five roles—information specialist, instructional partner, teacher, program administrator, and leader—while they participate in Sci-Dentity, a science-infused after-school program. We observed clear links between skills, dispositions, and responsibilities from the Standards, taught and facilitated by these school librarians, to principles in the Framework. We contend that the learning of the Standards is crucial to creating and sustaining science-learning environments as envisioned in the Framework and argue that school librarians’ role in science learning is more vital than it has ever been.