Despite the concerns regarding value-added models (VAMs), advocates hold strong to VAMs' theoretical strengths and potentials, while adopting a set of agreed-upon albeit "heroic" set of assumptions, without research in support. These assumptions transcend promotional, policy, media, and research-based pieces, but they have never been…

School districts across the United States increasingly use value-added models (VAMs) to evaluate teachers. In practice, VAMs typically rely on lagged test scores from the previous academic year, which necessarily conflate summer with school-year learning and potentially bias estimates of teacher effectiveness. We investigate the practical…