Washington — When it comes to judging teacher effectiveness, value-added models—statistical models that a number of states and districts have adopted to rate teachers based on student test scores—are too problematic to be of practical use and could unfairly hurt teachers who get assignments in struggling schools.
That was the heart of the message that one of the nation’s leading experts on educational testing and assessment delivered during a recent lecture on the pros and cons of value-added models, or VAMs.
“Teacher VAM scores should emphatically not be included as a substantial factor with a fixed weight in consequential teacher personnel decisions,” said Edward Haertel, Jacks Family Professor of Education, Emeritus, at Stanford University. “The information they provide is simply not good enough to use in that way.”
One major reason it is difficult to compare teachers fairly based on VAM scores is because of social stratification within America’s schools, Haertel said.
Some teachers, he said, may teach all low-achieving students from poor families while others may teach almost exclusively high-achieving students from affluent families.
“In the real world of schooling, students are sorted by background and achievement through patterns of residential segregation, and they may also be grouped or tracked within schools,” Haertel said, noting that achievement levels vary greatly among students from different schools. “Ignoring this fact is likely to result in penalizing teachers of low-performing students and favoring teachers of high-performing students, just because the teachers of low-performing students cannot go as fast.”
To bolster his point, Haertel noted how research has found that students from affluent families tend to make reading gains over summer vacation whereas students from low-income families tend to experience what is known as “summer loss.”
