The surge of support for the science of reading is cause for great cheer. According to the Albert Shanker Institute, 45 states and the District of Columbia have passed laws since 2019 to shift reading instruction based on what research says works. These laws often explicitly call for teaching phonics, phonemic awareness, and other skills that enable decoding of words. Implemented well, these laws will produce many more third graders who are strong decoders. But reading comprehension also requires students to have background knowledge--a rich store of content knowledge in history, geography, social studies, science, and the arts related to the topics students are reading about. And while a few of these states' laws (and only a few) mention background knowledge, no state gives it more than a passing reference. Yet the most important tool to build reading comprehension is a curriculum that charts a path--starting in the earliest grades--by which schools can intentionally build the content knowledge that constitutes background knowledge. That knowledge-building curriculum is essentially absent from American schooling. U.S. reading scores will rise and students will be better readers when they are learning from elementary curricula designed to build their background knowledge effectively. This article provides suggestions on how state boards can move this work forward.