This study assessed the perceptions and practices of a national sample of secondary school principals regarding reducing firearm violence in high schools. Data were collected via three-wave postal mailings. A 59-item valid and reliable questionnaire was mailed to a national random sample of 800 secondary school principals. Of the 349 principals (46 %) that responded, 17 % reported a firearm incident at their school in the past 5 years. Principals perceived inadequate parental monitoring (70 %), inadequate mental health services (64 %), peer harassment/bullying (59 %), and easy access to firearms (50 %) as the main causes of firearm violence in schools. The three barriers to implementing firearm violence prevention practices were: lack of expertise as to which practices to implement (33 %), lack of time (30 %), and lack of research as to which practices are most effective (30 %). Less than half of schools trained school personnel regarding firearm violence issues. The findings indicate that firearm incidents at schools may be more common than previously thought. A significant portion of principals are at a loss as to what to implement because of a lack of empirical evidence on what is effective. More research is needed to find the most effective school interventions for reducing firearm violence.