It's just another suggestion for a federal law that doesn't get to the root of the problem. If anything, it should be up to the states to set the security standards for their schools and then for each individual district to implement the state mandated security policy as the district sees fit. Whether that policy is arming teachers (not a good idea in my opinion), paying for an officer at each school (like Steve said, we have them here in NJ), or just by stepping up physical security. And physical security is where I feel we could make the greatest difference.
For work I am in and out of Gov't buildings, schools, and businesses ranging from mom and pop stores to Corporate offices. Besides the mom and pop stores, who are normally retail and have to have an open door policy, the second easiest place to get into is a school. Ring the buzzer, state company name (if they even ask), and I'm in. Free to wander the halls if I choose. I don't, I go straight to the office, if I can find it. Only there do I get asked what the nature of my visit is, for ID, and who I need to see.
To get access into most businesses it normally goes one of two ways. The first involves the getting buzzed in by the receptionist who is sitting right on the other side of the door and can see me. Before getting buzzed in, I'm asked who I'm there to see, and who I'm with. Once in the receptionist calls my contact and I stand and wait until the contact comes and escorts me everywhere. The second way is when there is no receptionist. I stand out in a locked vestibule, call my contact explain my business, and wait for the contact to come let me in and escort me. No remotely buzzing someone in.
See the problem? I'm not advocating making schools into prisons, but I feel schools could have a one time expense for upgrades to their physical security and be much safer then they were. There will be times when part of that security plan calls for an officer (example... old school with no ac so must have open windows). We are never going to completely eliminate these mass murders, but we can deter them and mitigate the risks.