In addition to the hockey puck tactic, the "rush at the shooter with a stapler or a book" has promise, too. If a book isn't at hand, perhaps throw your 50-page CV at the shooter?
Link: https://www.detroitnews.com/story/news/local/michigan/2018/11/27/oakland-university-fight-shooters-hockey-pucks/2129433002/
You are a teacher, right? What do you think of arming teachers with Tasers (with yearly training)?
(no message)
(no message)
(no message)
(no message)
(no message)
(no message)
Voiceover: When an active shooter enters your school what do you do?
{Unnamed student reaches into pocket and holds up a hockey puck}
Unnamed student: You get the puck out!
(no message)
(no message)