It’s been five years since the nation’s worst school shooting took place at Sandy Hook Elementary School, killing 20 children and six staff members. The massacre did not, as some had hoped, become a transformative moment and lead to widespread policies restricting gun access. But the Connecticut killings did lead many school districts across the country to ramp up security measures, including lockdown drills, hiring police officers and installing cameras and metal detectors. Under federal law, schools are designated gun-free school zones unless there’s an exception created by state law. Now, gun-rights advocates in a growing number of states are lobbying for such legislative changes, which would then allow educators to carry concealed weapons in classrooms. The efforts have sparked considerable controversy and many organizations, including those representing teachers, are fighting such measures, saying that arming school staff will help keep kids safe.