...kill eachother for survival? I need to know the name of this movie..

Ok they are school kids and they get kidnapped by thier teachers and are forced to kill eachother on an island, they all get a bag with a random weapon inside it and they have explosive collers around thier necks so if anyone is left apart from the winner they will die or if they try to touch the coller it will go off,

please help me find this film