For educators, the content of the curriculum really is like oxygen: it is the necessary precondition for improving schools, closing the achievement gap, engaging parents, and preparing teachers. However, when educators take the content of the curriculum for granted, they lose opportunities to coordinate and collaborate. Good curriculum instruction should be carefully planned to introduce topics early, and then teachers can intentionally revisit, deepen, and extend learning on these topics in later grades. This article presents the "Core Knowledge Language Arts" (CKLA) program that begins with preschool through third grade reading models to assist teachers incorporate a curriculum that helps students get the mastery for fluent reading, writing, and language comprehension. The program contains seven units, each with a teacher guide. Students and teachers engage in activities that build and deepen background knowledge using teaching practices that are appropriate for young children and early educators. The CKLA domains are carefully organized to build on each other within and across grades, giving students opportunities to refine and expand their knowledge and vocabulary over time. Included with this article are two sidebars: (1) Content on the Cutting-Room Floor: A Brief History of the Elementary Curriculum (Ruth Wattenberg); and (2) Preschoolers to Presidents: CKLA Builds Knowledge Step by Step.