Sounds like your emotions have gotten the better of you. Guns of every kind where already banned from schools yet that guy walked right in there, disregarding the law and killed people.
Also we the general population need and are guaranteed to be able to posses assault style, large compacity weapons just in case we need to overthrow our despotic government, its is our right and our duty to do just that. This is laid out in the Declaration of Independance and is guaranteed through the Second amendment of the Constitution.
" That to secure these rights, Governments are instituted among Men, deriving their just powers from the consent of the governed, --That whenever any Form of Government becomes destructive of these ends, it is the Right of the People to alter or to abolish it, and to institute new Government, laying its foundation on such principles and organizing its powers in such form, as to them shall seem most likely to effect their Safety and Happiness. Prudence, indeed, will dictate that Governments long established should not be changed for light and transient causes; and accordingly all experience hath shewn, that mankind are more disposed to suffer, while evils are sufferable, than to right themselves by abolishing the forms to which they are accustomed. But when a long train of abuses and usurpations, pursuing invariably the same Object evinces a design to reduce them under absolute Despotism, it is their right, it is their duty, to throw off such Government, and to provide new Guards for their future security "
So with gun bans out of the question lets talk about the real and actual problem...the PEOPLE who do these horrible things.