The students act it up. I had to play up a broken wrist. Running and screaming would be what you see if it was real. Imagine if a student went running by a swat member and startled them coming around a corner. This in real life is not just a small amount of kids but hundreds if not more in larger cities. While it wouldn't be safe to train with a full school of students at least they get practice in the field. Schools out for summer.. there empty.. and i'm sure free for them to use. Plus they used mini paintballs basically and kids had eye protection on. Seemed safe to me. I play paintball and they don't hurt.

this from the last line of his first link:
"Officials debrief each group after their simulations to talk about what they've learned, and how to improve. "

Its like learning CPR before you actually have to use it on someone. CPR can save a life if practiced but its not 100% you'll be a-ok. With better training you have a better chance.