There is a growing body of research on the validity and reliability of value-added measures, but most of this research has focused on elementary grades. Driven by several federal initiatives such as Race to the Top, Teacher Incentive Fund, and ESEA waivers, however, many states have incorporated value-added measures into the evaluations not only of elementary teachers but of middle and high school teachers as well. Almost all states have committed to one of the two Common Core assessments that will test annually in high school, and there is little doubt that value-added will be expanded to the grades in which the new assessments are introduced. In order to assess value-added and the validity and reliability of value-added measures, it is important to consider the significant differences across grades in the ways teachers' work and students' time are organized. This document provides evidence that there are differences in the validity of value-added measures across grades for two primary reasons. First, middle and high schools "track" students; that is, students are assigned to courses based on prior academic performance or other student characteristics. Tracking not only changes our ability to account for differences in the students who teachers educate, but also the degree to which the curriculum aligns with the tests. Second, the structure of schooling and testing vary considerably by grade level in ways that affect reliability in sometimes unexpected ways. The problems are partly correctable, but, as shown herein, more research is necessary to understand how problematic existing measures are and how they might be improved.