By Steven Glazerman, Dan Goldhaber, Susanna Loeb, Douglas Staiger, Stephen Raudenbush, and Grover Whitehurst
Commentary

The vast majority of school districts presently employ teacher-evaluation systems that result in nearly all teachers’ receiving the same (top) rating. For instance, a recent study of 12 districts in four states by the New Teacher Project revealed that more than 99 percent of teachers in districts using binary ratings were rated satisfactory, while 94 percent received one of the top two ratings in districts using a broader range of ratings. As U.S. Secretary of Education Arne Duncan put it during his bus tour this fall, “Today in our country, 99 percent of our teachers are above average.”

The reality is far different from what the evaluation systems suggest. We know from a large body of empirical research that teachers differ dramatically from one another in effectiveness. That today’s evaluation systems fail to recognize these differences means that the many important human-resource decisions are not as efficient or fair as they could be if they incorporated data that meaningfully differentiated among teachers.

Newer teacher-evaluation systems seek to incorporate information about individual teachers based on value-added measures of a teacher’s contribution toward student achievement. The teacher’s contribution can be estimated in a variety of ways, but typically entails some variant of subtracting the achievement-test scores of a teacher’s students at the beginning of the year from their scores at the end of the year, and making statistical adjustments to account for differences in student learning that might result from student background or schoolwide factors outside the teacher’s control. These adjusted gains in student achievement are compared across teachers.

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