This chapter discusses the role that poverty plays in the achievement scores obtained on various reading tests taken by US students. It describes that there is no escaping the powerful context, cohort, peer, or compositional effects on aggregate assessment scores when we measure reading, science, and mathematics. In the society teacher effects on aggregate scores are overimagined, and cohort effects are underemphasized: The problem of not recognizing these facts is to make policy that is wrongheaded, at best, and harmful at worst. An example of this is the spread of Value-Added Models—VAMs—in which teachers are held responsible for student test score growth. The analyses that teachers have little power to make big differences in aggregate scores, though occasionally they do. Teachers affect the test scores obtained by individual students more than they do the reading test scores of classes, and they have even smaller effects on the test scores obtained by schools and other larger aggregations of students.