A summary from the Everytown report "The Impact of Active Shooter Drills in Schools"

"Active shooter drills in schools are associated with increases in depression (39%), stress and anxiety (42%), and physiological health problems (23%) overall, including children from as young as five years old up to high schoolers, their parents, and teachers. Concerns over death increased by 22 percent, with words like blood, pain, clinics, and pills becoming a consistent feature of social media posts in school communities in the 90 days after a school drill. "

https://everytownresearch.org/report/the-impact-of-active-sh...

This is a very unreliable report from an anti-firearms activist group. Hardly a neutral source to be believed.

I dug into it more and found the lab who conducted the study at Georgia Tech published their results in a reputable journal with peer review (https://www.nature.com/articles/s41599-021-00993-6). The analysis seems fairly evidence-based, consisting of "54 million social media posts, both pre- and post-drills in 114 schools spanning 33 states."

I've heard of school districts doing simulated shootings with BB guns, masked men going through the halls to shout at the students, etc. That seems like needlessly frightening theater for no real gain (and might confuse the students ,at that )