Bombmaniac is right. They shouldn’t be throwing anything out of the window at pple! You could have gone into the school and spoken to the school guard and reported it. You might not have known, but at the entrance of any PS, there is a guard having pple sign in if they are there to see someone. You are right to be upset about the seforim, but they could have really hurt someone by throwing any object out of the window at pple’s heads. Of course, hindsight is 20/20.