Should Value-Added Models Weight All Students Equally?

Teacher value-added is used to evaluate teachers in many places. Implicitly, teacher value-added measures place equal weight on improvements in test scores, regardless of whether that improvement is from low to medium proficiency or from medium to high. However, increasing test scores may not be equally important for low achieving students as high achieving students. My goal is to ask whether information about which specific students a teacher helps most can help predict which teachers will produce specific outcomes for students. These outcomes include high school graduation, absence and disciplinary records, and grades in subsequent years.