Kendrick Castillo - only days from graduation - acted fast inside of his British literature class at a suburban Denver school Tuesday afternoon. And he paid with his life.

When a gunman burst through the door at STEM School Highlands Ranch, barking at students to stay in place and not move, Castillo, 18, rushed the shooter. It was a quick-thinking move that fellow students said gave them a chance to bolt for safety or take cover under desks.

"Kendrick lunged at (the gunman), and he shot Kendrick, giving all of us enough time to get underneath our desks, to get ourselves safe, and to run across the room to escape," senior Nui Giasolli told NBC's Today on Wednesday morning. Other students helped Castillo tackle the shooter, classmates said.