This article uses empirical data to consider the consequences of particular characteristics of instruction and testing in high school for the modeling and estimation of value-added measures of school or teacher effectiveness. Unlike Mathematics and Reading for most elementary and middle school grades, there is a lack of annual testing of students in all secondary grades and subjects. The development of value-added models in high school is complicated by the resulting unavailability of direct measures of prior knowledge and readiness of the student for the relevant course. Another distinction between high school and earlier grades is the presence of greater differentiated instruction in high school caused by supplemental course requirements or by student self-selection into different courses. We show that the traditional value-added model used in NCLB grades and subjects can be generalized to the high school context. Specifically, prior-year test scores in related or core subjects can be used to control for differences in student aptitude for the course or subject being evaluated. Similarly, we can account for relevant differences in classroom characteristics--such as the average prior achievement of the students in the classroom--if they are assumed to be beyond a teacher's control.