Dimensions of teacher quality in general and special education

The quality of a school’s teaching staff is its most important instructional resource, and teacher effects account for the largest variance in student achievement. Multiple studies have demonstrated that teachers account for approximately 7%–21% of the variance in student performance (Goldhaber, 2002; Nye, Konstantopoulos, & Hedges, 2004; Rivkin, Hanushek, & Kain, 2005). Over the past two decades, a large number of research studies have been undertaken to establish linkages between teacher characteristics, teacher knowledge, and observed classroom practice, on the one hand, and student achievement, on the other. The majority of these studies have focused on the value-added contribution teacher qualifications (e.g., experience, initial preparation, subject matter preparation, academic ability) make to student achievement, as teacher qualifications are easy to measure, are thought to constitute one dimension of teacher quality (i.e., credentials), and are accessible via state and national databases (Kennedy, 1992).