The debate over class sizes in schools has been a main feature of educational systems across the world. A speciﬁc and prominent feature of the educational policies of many western and eastern countries and cities has been a drive towards some form of reduction in class sizes and the commonly stated reason for this in both the east and west is to improve the quality of education. The policy seems simple enough but on closer inspection there are signiﬁcant differences in the deﬁnitions, rationale, and objectives between east and west. These differences are due to the diverse historical, socio-cultural and political contexts within which class size policies are implemented (Lai, 2011). Governments, international bodies and researchers have often overlooked these contextual differences when they compare class size policies and class size effects, and this can lead to considerable confusion. As Crossley (2010, 2012) contended, contextual factors are too frequently overlooked in comparative and international research in education, and comparisons of policy often overlooked the realities of practice in real educational contexts. A main purpose of this chapter is to seek clariﬁcation over the different contexts and ways in which class size reduction policies have been implemented.