Intergenerational mobility: mobility across generations or over the course of a single life time. People in the lowest and highest classes are the least mobile - the middle class is most likely to mobile, more or less equally upward or downward. Structural mobility or structural expansion: most upward mobility is due to increases in the size of the higher class through economic growth. The highest income groups tend to maintain their advantage even in the face of structural shrinkage, which result in more downward mobility for the middle classes. Structural mobility: does not require the displacement of an incumbent, but is made possible by the creation of additional positions, typically through organizational or economic growth. The growth of the middle class determines a society"s mobility rates, regardless of that society"s dominant culture of religion. Correlated disadvantage model: multiple disadvantages compound the problems associated with poverty. The strength of weak ties as a bridge.