i mean they probably ran for cover, called the police/their families then started posting stuff...
unless they got pics from inside the cafeteria and the guy shooting people??? @__@
"Just heard gunshots!" - obviously tweeted while it was happening
Then AS they were being evacuated out of the school they were taking pictures and trying to be the first to post stuff. It's so obvious they want to be the first person to tweet everything just to get attention. That's why I can't stand twitter. I'm just randomly reading a bunch of people's twitters from that school and they feel the need to put everything they know and put the most pointless things.