As discussed briefly in the previous chapter, research evidence has confirmed the importance of quality teachers to student learning (OECD, 2009a, 2005). Research in the United States dating back almost 20 years found that students whose teachers are at the top of the effectiveness range achieve as much as an additional year of growth in learning when compared with those students whose teacher is near the bottom of the range (Hanushek, 1992). In another often cited study based on data sets from Tennessee, United States, researchers found that if two similarly performing students in Grade 2 of primary school are assigned to high and lowperforming teachers for each of the subsequent three years, the difference in their performance at the end of the three years may be as much as 54 percentile points (Sanders and Rivers, 1996). The most recent thinking regarding effective educational systems has confirmed that the quality of an educational system cannot exceed the quality of its teachers (OECD, 2009a; McKinsey & Company, 2007). In the face of increasing international competition and economic downturn, however, governments are increasingly being forced to do more with less. In addition to attracting and retaining the most qualified professionals into the teaching profession, one important challenge becomes how educational systems can motivate and support teachers already in service to improve performance and increase student achievement.