It only takes one well placed bullet to take out anyone. IF a teacher had been trained to shoot well and accurately, if said teacher had access to a fire arm that was placed in a safe zone where no child had access but was easily obtained when needed, if a teacher had the opportunity to get off one well placed shot then yes it would have stopped this man before he could have taken more lives. The fact that the young man had many guns and a lot of bullets means that he intended to do just what he did do. To kill everyone he could before the police got to him. He could not shoot every gun at once . That is common sense. He choose small children . He was a coward.