National policies have targeted widespread exclusionary discipline in schools which is associated with negative academic outcomes. Principals play an important role in making disciplinary decisions, yet little is understood about how their mindsets might impact these decisions. We hypothesized that principals’ mindsets regarding the purpose of discipline (exclusion vs. prevention) would predict their responses to misbehavior. In a random, nationwide sample ( N = 234), principals responded to misbehavior by a hypothetical Black or White student. Exclusion beliefs predicted more severe discipline, whereas prevention beliefs predicted greater endorsement of referring the student to a school counselor. Principal mindsets also predicted exclusionary discipline in real-world contexts.