Too many policymakers have recently adopted the misguided belief that improvements in students' scores on standardized tests in mathematics and reading can be heavily relied upon to evaluate, reward, and remove the teachers of these tested students.

However, even the most sophisticated use of test scores, value added modeling (VAM), is a flawed and inaccurate way to judge whether teachers are effective or ineffective.

The heavy use of VAM in a teacher evaluation system will misidentify large numbers of both effective and ineffective teachers. Leading authorities (such as the Board on Testing and Assessment of the National Research Council of the National Academy of Sciences, the National Academy of Education, and researchers from RAND and the Educational Testing Service and a recent Economic Policy Institute paper by a group of prominent scholars, Problems With the Use of Student Test Scores to Evaluate Teachers) concur that VAM is too inaccurate to be used as the primary way to evaluate teachers. Most uses of test scores in teacher evaluation, in practice, actually fall far short of the flawed VAM measures because of a lack of appropriate data and the adoption of weaker statistical methods.

Adopting an invalid teacher evaluation system and tying it to rewards and sanctions is likely to lead to inaccurate personnel decisions and to demoralize teachers, causing talented teachers to avoid high-needs students and schools, or to leave the profession entirely, and discouraging potentially effective teachers from entering it. Educational outcomes will suffer as a consequence.

Besides concerns about the accuracy of statistical methodologies, other practical and policy considerations weigh against heavy reliance on student test scores to evaluate teachers. Research shows that an excessive focus on basic math and reading scores can lead to narrowing and over-simplifying the curriculum to only the subjects and formats that are tested, reducing the attention to science, history, the arts, civics, and foreign language, as well as to writing, research, and more complex problem solving tasks.

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.

Legislatures should not mandate and districts should not pursue a test-based approach to teacher evaluation that is unproven and likely to harm not only teachers but the children they instruct.