What started the WW2 Genocide?

My teacher said that it FIRST started out in Bosnia, in a Middle School.. or something like that. Yes, I know about Adolf Hitler and stuff. He just said that the very first start was killings in a middle school. Is that correct and if so could you give me some information and some sites I can visit. And if it is not correct, could you correct me where I am wrong. Thanks. I would like to read up on this, so if you could recommend some sites and stuff... Thanks.