I wholeheartedly believe in discipline without punishment (or rewards), but you are 100% right: everyone involved needs to be trained and know what is happening. Isn't it typical of our schools to do this to teachers? "Stop teaching this way now. We don't have the new materials for you yet, but just start teaching the new way. Training will come later." Then when it doesn't go well everyone decides the new way was "unsuccessful."

Even when you have restorative practices or positive discipline in place, that does not apply to a shooting! I used all kids of conflict resolution and positive methods to get through the typical classroom issues. However, when things like sexual harrassment came up, I got the principal and the parents involved. One year it was a boy and one year it was a girl. They were each suspended for a day or two. This was a 5th grade class and I didn't feel comfortable discussing that issue with all of the 10-year-olds.