Well, this was different. She chose an answer from a list: Sometimes.

This class feels like a happy family.

She arched an eyebrow. Was this a joke? Totally untrue.

In towns around the country this past school year, a quarter-­million students took a special survey designed to capture what they thought of their teachers and their classroom culture. Unlike the vast majority of surveys in human history, this one had been carefully field-tested. That research had shown something remarkable: if you asked kids the right questions, they could identify, with uncanny accuracy, their most—and least—effective teachers.

The point was so obvious, it was almost embarrassing. Kids stared at their teachers for hundreds of hours a year, which might explain their expertise. Their survey answers, it turned out, were more reliable than any other known measure of teacher performance—­including classroom observations and student test-score growth. All of which raised an uncomfortable new question: Should teachers be paid, trained, or dismissed based in part on what children say about them?

To find out, school officials in a handful of cities have been quietly trying out the survey. In D.C. this year, six schools participated in a pilot project, and The Atlantic was granted access to observe the four-month process from beginning to end.

At McKinley, a magnet school for science, technology, engineering, and mathematics, Nubia Baptiste filled in bubbles in response to all 127 questions. Then she slipped the survey into the envelope provided and sealed it.

Afterward, in the hallway, she tried to understand what had just happened. It didn’t fit with her previous experience. “No one asks about the adults,” she said. “It’s always the student.”

A classmate standing next to her shook her head. “They should’ve done this since I was in the eighth grade.”

For the past decade, education reformers worldwide have been obsessed with teaching quality. Study after study has shown that it matters more than anything else in a school—and that it is too low in too many places. For all kids to learn 21st-century skills, teaching has to get better—somehow.

In the United States, the strategy has been for school officials to start evaluating teacher performance more frequently and more seriously than in the past, when their reviews were almost invariably positive. The hope was that a teacher would improve through a combination of pressure and feedback—or get replaced by someone better. By the beginning of this year, almost half the states required teacher reviews to be based in part on test-score data.

So far, this revolution has been loud but unsatisfying. Most teachers do not consider test-score data a fair measure of what students have learned. Complex algorithms that adjust for students’ income and race have made test-score assessments more fair—but are widely resented, contested, or misunderstood by teachers.