It was 45 seconds too late, but the teacher had a plan.

A gunman had just barraged her classroom with an AR-15, killing two students and injuring four others before turning to a classroom across the hall. The bullet-riddled walls were crumbling. Ceiling tiles were falling. If the shooter came back to kill more of her students, the teacher decided, she would stand up and shout, “We love you.”

The teacher was Ivy Schamis, whose husband would be waiting at home with a Valentine’s Day dinner; whose son was planning a wedding she couldn’t imagine missing; whose curriculum for this class — History of the Holocaust — had just moments earlier stirred a discussion about hate on campuses.

We love you. These would surely be her final words, Ms. Schamis thought. She knew her plan was futile — irrational, even. But with no stop-the-bleed kit, no shield, no help, words were all she had to show the children that an adult had put up a fight.

The moment never came. The gunman doubled back to the class across the hall, but not to Room 1214. At the command of a SWAT team, Ms. Schamis climbed over bodies and ran with her surviving students down the blood-smeared hallway, out the doors, and into the blinding light.

What waited for her there, in the days and months and years ahead, would be a whole new role in the lives of the 30 students who had survived. For them, she would be what she couldn’t be for the two who died: a lifeline.