Value-added models (VAMs) are used to measure changes in student achievement on large-scaled standardized test scores from year to year. When aggregated, VAM estimates are used to measure teacher effectiveness and hold teachers accountable for the value they purportedly add to or detract from student learning and achievement. In this study, researchers examined the extent to which purposeful (nonrandom) and random assignment of students into classrooms occurs in Arizona elementary schools (Grades 3-6). Researchers found that overwhelmingly, students are not randomly assigned and administrators, teachers, and parents play a prodigious role in the process. Findings have current implications for value-added analyses and the extent to which nonrandom assignment practices might impact or bias teachers' value-added scores.