I thought he chained some of the doors?
Yes, he chained the doors to the classroom building. But nobody knew that till SWAT had assembled, stacked and tried to rush the doors. Then they had to go look for something to cut the chains with.
For a very brief moment there was some effort to teach elementary-school aged kids to throw books at and bum-rush the armed intruder. Apparently some adult then figured out that teaching the kids how to take down an armed assailant might transfer to taking down a not-popular teacher/administrator so the program died.
Huddle up, folks. Just like the fishies in the center, you can lessen the chance that
YOU will be killed even though someone is going to buy the farm.
stay safe.