Testing the metrics
In recent years, 14 states in the U.S. have begun assessing teachers and schools using Value-Added Models, or VAMs. The idea is simple enough: A VAM looks at year-to-year changes in standardized test scores among students, and rates those students’ teachers and schools accordingly. When students are found to improve or regress, teachers and schools get the credit or the blame. Perhaps not surprisingly, however, VAMs have generated extensive debate. Proponents say they bring accountability and useful metrics to education evaluation. Opponents say standardized tests are likely to be a misleading guide to educator quality. Although VAMs often adjust for some differences in student characteristics, educators have argued that these adjustments are inadequate. For example, a teacher with many students trying to overcome learning disabilities may be helping students improve more than a VAM will indicate. A new study by an MIT-based team of economists has developed a novel way of evaluating...