I'm not sure about the causes, but it seems in the UK for example that social mobility has decreased in the past few decades compared to the 1960s. A big part of that has been the disaster of comprehensive education - the old grammar school system, which selected children from poorer families, gave at least some a chance of climbing the social ladder. Comprehensive schools are more of a lottery than a meritocracy, and the wealthy as always have the option of fee-paying "public" schools.