As a British person, this kind of shit blows my mind. We had a school shooting at a place in Scotland called Dunblane in 1996, 16 children died. No one called for Armed Guards, guns were outlawed and people willingly handed in their guns, Hell, our police arnt even armed on the majority, with special police armed response units in each force.
Yet, yours is a slightly more difficult and pressing problem, especially as America is huge and collecting all the guns would be a huge task, yet, something needs to be done and now is the time.