Limited research has been conducted on the state-level factors that may be associated with intentional school shootings. We obtained school shooting data from the "Washington Post" that identified any act of intentional interpersonal gunfire in a K-12 school over the course of two decades. We also compiled new data on active school shootings during the same twenty-year time period, which identified any attempted mass shooting incident in a K-12 school. We conducted a time-series analysis to measure the association of permissiveness of state firearm laws and state gun ownership with K-12 school shootings and active shootings. More permissive firearm laws and higher rates of gun ownership were associated with higher rates of both school shootings and active school shootings after controlling for critical covariates. Specific recommendations for K-12 schools to consider as they seek to prevent acts of intentional gunfire on school grounds are presented.