Students' Fortunes Rest With Assigned Teacher

By Jeff Archer

At a time when efforts to tie teacher evaluations more closely to student performance appear to be gaining momentum, one of the nation's biggest school districts believes it has found another compelling reason to build such a link.

Researchers in the Dallas district have shown that having a less effective teacher can significantly lower a student's performance over time, even if the student later gets more competent ones. And while new evidence that the students of good teachers tend to perform better might not seem surprising, district officials were struck by just how much teacher quality mattered to student achievement.

"This is the first time we've measured teachers' effects on the ability of kids to perform on assessments," said Robert Mendro, the district's executive director of institutional research. "And what surprised us the most was the...