There was a dramatic drop off according to their own data in 1993
In 1994 the assault weapon ban was enacted (correlation implied by myself without looking at data)
Ban was lifted in 2004
According to their own data there was a dramatic spike again (correlation implied by myself without research)
Things started to decline again, but have been trending up since 2011 according to their data.
That time period includes sandy hook, that data does not include all of the shootings this year.

Furthermore when it comes to murders at school by guns, why should it only be of concern when it's an epidemic?

The article writer implies that more kids die from drowning and bike accidents
Are we not making safer biking areas, are cpr classes not offered, are dangerous swimming areas not marked?

I hate people writing about data that they don't understand. Or writing about stats when it comes to mortality. Cultural conversations drive actions and reactions. Stats don't drive that convo. And right now our culture is screaming out enough.