Two things

First of all, more gun control would have made no difference. The fact is that anyone who wants an item -- really wants it -- can get it regardless of what the law says. See also: prohibition.

Second of all, concealed carry would have made no difference either. The odds that someone with a concealed carry license would have been in the classroom, ready, and actually able to take out the shooter is somewhere in the realm of near fantasy.

To summarize, although people on both sides of the gun issue will certainly try to make hay out of this event, the fact is that both sides really have nothing useful to add. The shooting today was an outlier, and a tragedy, and you don't make public policy choices based on outliers.