Controversies have erupted in recent years over the teaching of critical perspectives in United States K-12 schools, particularly related to issues of diversity, race, gender, and sexuality. These tensions have resulted in attacks on critical curriculum, with nearly one-third of states banning curriculum that offers critical views of the racial past of the U.S. and over 200 bills introduced in 40 states that would restrict curriculum related to diverse topics. In this study, we apply a knowledge mobilization framework to examine what and whose knowledge is being restricted in U.S. K-12 schools, and how and why this is happening. Our findings indicate that in 16 Republican-dominated states, policies have been enacted to restrict the teaching of critical perspectives on race, sexuality, and other controversial subjects and to perpetuate a positive view of U.S. history. The study sheds light on the prevalence, underlying nature, and consequences of these educational policies.