Teacher quality with regard to student achievement—also known as "teacher effectiveness"—is measured in terms of student achievement gains. Most extant research on teacher quality pertains to observable attributes, preparation, and credentials (Goldhaber, 2002; McCaffrey et al.,2003; Neild and Ripple, 2008). Probably the most widely studied attributes are experience and education levels, in part because the data can be readily obtained because of their use in salary placement (Goldhaber, 2002).