School shootings and other mass killings have had a major political impact. Governments have discussed gun-control laws, to increase time for background checks. Also, bulletproof school supplies have been created, including backpacks, desks, bullet-resistant door panels, and classroom whiteboards (or bulletin boards) which reinforce walls or slide across doors to deflect bullets. Another organization that has proposed possible solutions to school shootings is the National Rifle Association (NRA), to allow teachers to carry weapons on school grounds as a means of protecting themselves and others. So far, ten states have already introduced legislation to allow weapons on school property with eighteen states already allowing guns to be carried on school grounds, but not without constraints. Most states also require the gun carriers to receive advance permission from the districts' superintendents or trustees. "In New York State, written permission from the school is required in order to carry a firearm on school grounds."