In October of my second year teaching, the principal called me into his office to meet with a tenth grader. Eyes averted, in a low and quivering voice, the student told me, “I feel like you always get on my case.”

“I’m sorry if you feel singled out,” I said. “When a group is distracted, I tell everyone to get to work.”

“No,” she said forcefully, straining for words. “If there’s like four people talking, you always call my name, and then tell us to get back to work.”

To my surprise, I realized it was true: The same morning, I’d done exactly that. And two days earlier, too. I’d been experimenting with group work in her class, and I hadn’t yet calibrated my mental detector for “noisy and productive” versus “noisy and distracted.” I knew it was a problem. For weeks, I’d been spinning like a weather vane, letting the class slide out of control and then snapping at them. Or so I thought. It now seemed that I wasn’t snapping at them—too often, I was snapping at her.

“Maybe you’re right,” I said at last. “I’m sorry about that. I guess I notice you more than others because I know you’re a strong math student, and you’re struggling in the class. So I worry.”

“But I’m trying,” she said, close to tears, and I realized I’d made a deeper mistake. I’d chalked up her lack of success to apathy, distractions, low effort—anything that would put the ball in her court rather than mine. With my attention split a hundred ways—the seniors flailing in calculus, the bio class I lacked the expertise to teach, the logistical tangles of running a homeroom—I’d been marking F’s on her quizzes without really considering the name at the top or how my class must look through her eyes.

I apologized again—sincerely, this time—and spent that night wondering how I’d been so oblivious to my own small cruelties.

The asymmetries of the classroom are intense. With each teacher responsible for a hundred students or more, the typical kid occupies a teacher’s thoughts for—at best—a minute or two per day. But each student only has a handful of teachers. Every instructor looms large in her world, wielding power over her days, via class periods; her nights, via homework; and her future, via grades. She spends much of her time thinking about the teacher’s demands, the teacher’s expectations, the teacher’s preferences and inconsistencies.

So when a teacher briefly focuses attention on a particular student, it comes with the heat and intensity of a spotlight. A moment the teacher barely remembers might stick with the student for years.

This was a frightening realization for me. Classroom lessons may slip quickly through students’ fingers, but the classroom experience lingers in memory. Each teacher offers students a different model of authority and justice. We set our own standards of fairness and sometimes fail to honor them. A teacher swings a heavy club, and we can leave big, purple bruises if we’re not careful.