Students at Evergreen High School in Colorado were more than halfway through the school day in their third week of classes this semester when over 100 law enforcement officers swarmed the campus, searching every room for an active shooter as they went into lockdown.

At least two students have been wounded in a shooting at a suburban Denver high school, authorities said Wednesday.

For nearly three decades, Colorado has experienced some of the highest-profile shootings in the nation – tragedies that claimed the lives of ordinary Americans sitting in classrooms or movie theaters...