A WEEK and a half ago, the day after the school shooting near Cleveland, a student stood in the doorway of my Bronx college classroom. He was eating half a bagel with cream cheese. It was a month into the semester, 45 minutes into the class period. I didn’t remember ever having seen him before.

He had been staring into my room, watching us through the small rectangular window next to the heavy metal door. He seemed to be looking for something. I motioned to him. He opened the door and said he wanted to talk to me.

I was tight on time, trying to finish discussing a chapter before giving a test the next time the class met, so I refused. But before I could tell him to e-mail me or wait to talk after class, he said, in front of all the students, “Something big is going to go down at the test.” Then he disappeared.

All I could think of was Cleveland.

Every time I hear about a school shooting — whether in a college, like the Virginia Tech massacre of 2007; a public high school, like last month’s attack; or a private academy, like the one in Jacksonville, Fla., where, on Tuesday, a fired teacher killed an administrator and himself — I say a silent prayer for the students and teachers who were injured or died. I think about their families and those who watched their peers mowed down, about the warning signs that may or may not have been there. And I wonder if it could happen to me.