As she does every day, Kay Cates asked her 10-year-old son how his school day went. He shrugged.
"We did math. We did reading. We had a lockdown," the Boulder fourth-grader replied.
She froze. When pressed, the boy matter-of-factly explained the protocol he has rehearsed since kindergarten: "We hid so in case a man with a gun came he can't find us."
That was Dec. 4. Nine days later, across the Denver metro area in Centennial, a man with a gun came to Arapahoe High School. Karl Halverson Pierson, 18, shot and gravely wounded another student before taking his own life. It was at least the fourth school shooting incident in the Denver area since 1999, starting with Columbine High School.