A growing number of school districts have adopted a system called value-added modeling to answer that question, provoking battles from Washington to Los Angeles — with some saying it is an effective method for increasing teacher accountability, and others arguing that it can give an inaccurate picture of teachers’ work.
The system calculates the value teachers add to their students’ achievement, based on changes in test scores from year to year and how the students perform compared with others in their grade.
People who analyze the data, making a few statistical assumptions, can produce a list ranking teachers from best to worst.
The Los Angeles Times recently produced just such a ranking:
The Los Angeles Times has produced an analysis of how effective Los Angeles Unified School District teachers have been at improving their students’ performance on standardized tests. The Times has decided to make the ratings available because they bear on the performance of public employees who provide an important service, and in the belief that parents and the public have a right to the information.
However, some researchers caution that judging teachers based on the output from value-added models requires careful analysis and consideration of the limitations of such models. This new report (PDF) by Baker et. al. notes:
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.
If you’re confused about exactly how valued-added modeling works but your don’t have access to an applied statistician, Dr. Edward Wiley of the U. of Colorado at Boulder has published this guide to value-added modeling for practitioners and interested laymen. Disclosure: I am a doctoral candidate at the U. of Colorado and have studied with Dr. Wiley in the past.