Here is a picture posted by Marc Sonnenberg.

It was taken 2 seconds before Reagan was shot. He was surrounded by Secret Service agents, who are some of the most finely trained gunmen and security experts we have in this country.

Hinckley fired a Röhm RG-14 .22 cal. blue steel revolver six times in 1.7 seconds, missing the president with all six shots.The first bullet hit White House Press Secretary James Brady in the head. The second hit District of Columbia police officer Thomas Delahanty in the back of his neck as he turned to protect Reagan.Hinckley now had a clear shot at the president,but the third overshot him and hit the window of a building across the street. As Special Agent In Charge Jerry Parr quickly pushed Reagan into the limousine, the fourth hit Secret Service agent Timothy McCarthy in the abdomen as he spread his body over Reagan to make himself a target.The fifth hit the bullet-resistant glass of the window on the open side door of the limousine. The sixth and final bullet ricocheted off the armored side of the limousine and hit the president in his left underarm, grazing a rib and lodging in his lung, stopping nearly 1 inch (25mm) from his heart.Had Parr hesitated for a moment, the president would likely have been hit in the head. [Wikipedia].

This is what it looked like a couple of seconds later:

After reading the account above, I do not think that a gun locked in a teacher’s classroom has any chance of saving lives. A trained armed guard ambling around the facility has little odds of being nearby where a shooting might take place. The teacher or the guard might save the 11th child from being mowed down, but not any of those covered by the first magazine in the shooter’s gun, provided the clip only holds 10.

And yes, this assassination attempt on Reagan on March 30, 1981 was by a mentally ill person.