What difference would it have made other than to a few judgmental people on this board? This guy was determined to harm innocents before killing him. He knew that he was not leaving the school alive. He was armed, the teachers and aides were not armed. Despite what is commonly shown in the movies, an armed man has an advantage over an unarmed female who was almost certainly smaller than him. It is very likely that the teacher's actions saved lives by not forcing his hand and have him start shooting everyone, including the boys and infants. From what I now of the Amish, their communities are very close and I am sure that the survivors are in agony right now over the deaths of those innocent girls.
I for one think that it is inappropriate to second-guess (and yes, it sounds like blame when you say things like "I would never leave the children behind) when this occurred four hours ago and we don't know all of the details.
I've seen events happen at my wife's school that she could handle and resolve that first or 2nd year teachers were completely inept at. (I know in this case we're talking about a killer who wanted to die).
Maybe the nature, age, maturity, etc of the teacher there was a factor in the outcome. And maybe not. We're just speculating.
It's just a sad thing either way.