Can someone explain to me why school shootings seem to happen in waves????

Think about it, it seems like everytime on school shooting happens a bunch of others quickly follow. I dont know if kids see all the other attention that kids who shot up a school got and then do it themselves??? Why would that matter. But on the other hand that does not matter, any kid that shoots up a school will get front page attention nationwide. It doesnt matter if your the first, last, or any where in between. I'd really like to know why when one kid shoots up a school that a bunch of others follow. Its like kids sit waiting and wanting to shoot up their school, but wait until some other kid does it first before acting themselves. I dont get it, i really dont get it.