Value-added evaluations use student test scores to assess teacher effectiveness. How student achievement is judged can depend on which test is used to measure it. Thus it is reasonable to ask whether a teacher's value-added score depends on which test is used to calculate it. Would it change if a different test was used? Specifically, might a teacher admonished for poor performance or recognized for good performance have been treated differently if a different test had been used? It's an important question, particularly because most states will soon be adopting new tests aligned with the Common Core State Standards. In this knowledge brief the author discusses what is known about how sensitive value-added scores are to the choice of test and what more needs to be known. He also discusses issues about the choice of test that might not be resolved through empirical investigation, as well as the implications of these findings for states and school districts.