Florida's Broward County Public Schools and the University of Chicago engaged in a Research-Practice Partnership (RPP) to scale teacher practices that support students' critical thinking. As part of the RPP, Jeanne Century's research team conducted research to determine what barriers might limit the spread of these practices. The findings show that teacher biases about students' ability to engage in critical thinking, as well as their self-efficacy, might limit the extent to which teachers are willing to change their practices. Because teacher perceptions have been linked to students' race, gender, and socioeconomic status, these perceptions may have consequences for efforts to promote equity. To improve teacher perceptions, districts can change their messaging about student abilities, boost teacher self-efficacy, and directly address teacher perceptions.