A large body of studies examines the relation of teacher characteristics to student achievement, often referred to as teacher effects. Although teacher characteristics are defined with variation across studies, student achievement usually refers to a form of standardized achievement test (e.g., ACT). The goal of research on teacher effects is to identify effective teacher characteristics that promote growth (gains) in student outcomes. Researchers seek to determine the extent of the relation between teacher characteristics and student outcomes to establish an order of importance among teacher characteristics.