This report examines the validity of measures of teacher effectiveness from the Tennessee Value-Added Assessment System (TVAAS). Specifically, the report considers the following claims regarding teacher effects: that they adequately capture teachers’ unique contributions to student learning; that they reflect adequate standards of excellence for comparing teachers; that they provide useful diagnostic information to guide instructional practice; and that student test scores adequately capture desired outcomes of teaching. Our analyses of the TVAAS model highlight potential weaknesses and identify gaps in the current record of empirical evidence bearing on its validity.