In addition to the potential loss of life, school shootings can evoke feelings of profound fear and anxiety that disturb a community's sense of safety and security. Questions have been raised about whether schools' approaches to addressing student behavior are a factor in school shootings. These approaches include discipline that removes the offending students from the classroom or school, and preventative approaches meant to change student behaviors before problems arise. The Government Accountability Office (GAO) was asked to examine school shootings, including the link between discipline and shootings. This report examines: (1) the characteristics of school shootings and affected schools; and (2) what is known about the link between discipline and school shootings. To do so, GAO analyzed data on school shootings and school characteristics for school years 2009-10 through 2018-19; and conducted a literature review to identify empirical research from 2009 to 2019 that examined discipline approaches in school, and the effects of these approaches on outcomes of school gun violence, school violence, or school safety. GAO also interviewed selected researchers to gather perspectives about challenges and limitations in conducting research on school discipline and school shootings. Findings show that shootings at K-12 schools most commonly resulted from disputes or grievances, for example, between students or staff, or between gangs, although the specific characteristics of school shootings over the past 10 years varied widely, according to GAO's analysis of the Naval Postgraduate School's K-12 School Shooting Database. After disputes and grievances, accidental shootings were most common, followed closely by school-targeted shootings, such as those in Parkland, Florida and Santa Fe, Texas.