First you of all people must realize that most schools are very spread and it would take more than one armed individual to protect many schools. A policemen who responded to the Sand Hook shooting stated the shooter was so heavily armed that he felt he could have not stopped him. So we are talking probably tens of thousands of guards. Will the tea party pay for them. Then there are malls and thousands of other soft targets. So if you eliminate one soft target the shooter will go after another. To guard all of the soft targets you are talking hundreds of thousands of armed guards.
Now I see why the NRA wants to arm everyone.
Israel is a totally different. it has a population that is far less than the US and almost everyone is fully trained and part of the army reserve. They even keep their military weapons at home. Their weapons training is continuing and each individual is in the reserves and is overseen by a regular army NCO or officer. With all of these type of protection they still have had mass killings.