This paper conceptualises the inaction of school leadership teams in response to systemic sexual harassment as institutional gaslighting, a theoretical tool to date unutilised in studies of sexual harassment in educational settings. Drawing on case studies of two women teachers who experienced sustained sexual harassment in Australian schools, and whose leadership responded with denial, minimisation and intentional mixed messaging, we argue that schools are home to and perpetuate unequal epistemic terrains, where women's knowing is under­mined by dominant operations of the school that work to maintain structural and cultural norms. These norms, we suggest, are informed by hegemonic masculinity and feminine stereotypes of irrationality and deviance, and prevent violence against women in schools being addressed. We argue that institutional gaslighting is a productive concept to expose the epistemic injustice that delegitimates women's knowledge of their experience and help in addressing systemic issues with responding to sexual harassment in schools.