For years, educators have argued about the best ways to grade teachers’ performance in the classroom. Some skeptics doubted it was possible to fairly evaluate teachers, partly because some teachers had brighter students while others faced classes filled with struggling kids.

That argument should end, thanks to a blockbuster new study from the Bill & Melinda Gates Foundation.

Researchers tracked 3,000 teachers in Dallas; New York; Charlotte, N.C.; and elsewhere over three years. They found that the most effective teachers can spur test scores of students who had lagged under less effective teachers. Most important: The best teachers produced test score and other academic gains even when students were assigned randomly to their classrooms.

In other words, this research tells us that good teachers can help all students, not just those who excel naturally. Key point: Researchers showed they could reliably identify those teachers and predict their impact on student learning.

A combination of three measures yield the most accurate evaluations, according to the study:

* Students’ progress on standardized tests. That is the so-called “value-added” formula that shows how much a teacher catapults a student’s academic growth or sets it back. The study says student growth should be a third to a half of a teacher’s evaluation.

* Careful observations of teachers in front of their classes, either by principals or other trained observers.

* Surveys of students about what goes on in the classroom. Unsurprising conclusion: Kids often know which teachers are most effective.

Those three factors produced a result “teachers can trust,” Vicki Phillips, a director in the education program at the Gates Foundation, told reporters.

For principals, teachers and parents, the Gates study provides compelling evidence of how teachers may be judged fairly.

The Gates study should give educators confidence to set these gold-standard evaluation systems in place.

We know how to identify and reward the best teachers. And we know the result: Kids learn.

Editorial by the Chicago Tribune