Most public schools have a library, but little is known about their quality or content. I collect original data on hundreds of titles in over 6,600 school libraries to identify patterns in resources and content. Three main findings emerge. First, gaps in library resources/quality exist, especially between schools in low- and high-income areas. Second, although books with “controversial content” are widely available, their prevalence is related to local politics and social environments. Libraries in conservative areas are less likely to have books with LGBTQ+, race/racism, or abortion content and more likely to have discontinued Dr. Seuss and Christian fiction titles. Third, book challenges in the 2021-22 school year have had “chilling effects” on the acquisition of new LGBTQ+ content.