Populations of school-age children have shrunk in many OECD countries, while in others, enrolments in urban schools have swelled alongside internal migration to cities. Both situations have raised concerns about the quality and cost of small schools, particularly in rural areas. Rather than identifying an "optimal size", empirical studies indicate that the effect of school size varies across student groups and levels of education. In general, secondary school students tend to benefit more from larger schools than primary school pupils, and low-income and minority students appear to perform belter in smaller schools (Howley and Howley, 2004). Some studies also find evidence of diminishing returns to scale, suggesting that student performance improves up to a certain school size (which tends to be smaller in primary education than in secondary education) and declines thereafter. Many countries offset the higher cost of maintaining small schools by providing them with additional funding or promoting consolidation programmes to reduce the fiscal burden of a fragmented school network.