Answer:
Every classroom should have a well-educated, professional teacher, and school systems should recruit, prepare, and retain teachers who are qualified to do the job. Yet in practice, American public schools generally do a poor job of systematically developing and evaluating teachers.
Many policy makers have recently come to believe that this failure can be remedied by calculating the improvement in students’ scores on standardized tests in mathematics and reading, and then relying heavily on these calculations to evaluate, reward, and remove the teachers of these tested students.
While there are good reasons for concern about the current system of teacher evaluation, there are also good reasons to be concerned about claims that measuring teachers’ effectiveness largely by student test scores will lead to improved student achievement. If new laws or policies specifically require that teachers be fired if their students’ test scores do not rise by a certain amount, then more teachers might well be terminated than is now the case. But there is not strong evidence to indicate either that the departing teachers would actually be the weakest teachers, or that the departing teachers would be replaced by more effective ones. There is also little or no evidence for the claim that teachers will be more motivated to improve student learning if teachers are evaluated or monetarily rewarded for student test score gains.
A review of the technical evidence leads us to conclude that, although standardized test scores of students are one piece of information for school leaders to use to make judgments about teacher effectiveness, such scores should be only a part of an overall comprehensive evaluation. Some states are now considering plans that would give as much as 50% of the weight in teacher evaluation and compensation decisions to scores on existing tests of basic skills in math and reading. Based on the evidence, we consider this unwise. Any sound evaluation will necessarily involve a balancing of many factors that provide a more accurate view of what teachers in fact do in the classroom and how that contributes to student learning.
Evidence about the use of test scores to evaluate teachers
Recent statistical advances have made it possible to look at student achievement gains after adjusting for some student and school characteristics. These approaches that measure growth using “value-added modeling” (VAM) are fairer comparisons of teachers than judgments based on their students’ test scores at a single point in time or comparisons of student cohorts that involve different students at two points in time. VAM methods have also contributed to stronger analyses of school progress, program influences, and the validity of evaluation methods than were previously possible.
Nonetheless, there is broad agreement among statisticians, psychometricians, and economists that student test scores alone are not sufficiently reliable and valid indicators of teacher effectiveness to be used in high-stakes personnel decisions, even when the most sophisticated statistical applications such as value-added modeling are employed.
