School districts, individual schools, and education policies all contribute to student achievement. But it can be argued that the most important contributing factor is the quality of the teacher in the classroom. Evaluating teacher quality is complicated, yet it has become even more important with the testing and assessment focus of No Child Left Behind (NCLB). Teacher quality traditionally has been measured by considering "teacher characteristics," for example, the teacher's academic degrees, personality, and professional development activities. Recently, though, researchers and policy makers have begun to embrace a "value-added" approach to measurement. This set of statistical methods offers a more objective and more precise way to measure the value that teachers, schools, and districts add to students' educational experiences. But UW-Madison education professor Douglas Harris cautions that measuring teacher quality cannot result from choosing between the traditional "teacher characteristics" measure nor a simple value-added measure. Instead, it's necessary to use multiple measures, including formative and summative assessments. Evaluating and improving teacher quality requires a comprehensive strategy that few current or proposed policies provide. Evidence suggests that teachers should be rewarded not for their graduate degrees, but for a combination of experience, certain types of professional development, teacher value-added and school value-added. Current proposals shift away from the traditional "teacher credentials" strategy in favor of a value-added accountability strategy. New policies will fail if they only reinforce the limitations of the status quo, rather than facilitate innovation and success. Harris advocates an evaluation framework he refers to as "policy validity" which involves multiple measures.