Even if it is a turning point, it won't be very effective, if at all. Events like this are statistical outliers, ranging somewhere between uncommon and rare. I think what is difficult for people to acknowledge and handle is that there is no solution for "preventing mass school murder shootings from ever happening again." What there is are some measures that might reduce the frequency and the extent of damage when they do occur. Changes to address the latter have already occurred. Police responders respond differently by attempting to directly engage the perp instead of waiting for the SWAT team to arrive. Schools devise strategies and drills to reduce the number of victims, which it appears the folks at Sandy Hook did.

Bans on guns labeled "assault weapons" and large capacity magazines would reduce their availability to the criminally motivated over time, probably measured in decades, but instant results would be elusive.

Meanwhile it would be of greater benefit for folks to come to terms with the notion that the certainty they seek is not attainable, at any cost. And society is always concerned about cost. Reactionary measures, like TSA and Homeland Security feel good window dressing, as was done post-9/11, is not an effective alternative.