Over the last three decades, more than 260 million rural residents of China have moved to the cities in one of the largest migrations in human history.

Most have moved to cities because they cannot afford not to. For all of the economic growth in China, rural China is still a place of poverty. Almost half of rural residents live on less than $2 a day. Rural Chinese have less schooling, health care and income. They die, on average, more than 12 years earlier than their big city counterparts. Rural children are more than 5 times less likely to go to college than urban ones.

The migrants, who come to the city seeking a better life, have left behind an estimated 55 million children in the care of relatives or neighbors. Without their parents’ regular attention, these children face challenges on a number of fronts. Likewise, rural communities become less vibrant because of the absence of working-age people. What’s more, the remaining residents – mostly elderly parents and children – need to shoulder much more of the agricultural work and daily chores.

Migrants who move with their children face a host of other challenges, including enrolling their children in school. Many schools regard prior education background as an important criterion and will not admit children educated in rural schools – often considered inferior.

Rural residents cannot sell or mortgage their homes or the land under them, which means they often arrive in the city without any nest egg. This consigns them to “urban villages” — areas with poor infrastructure, bad facilities and cheap rent.

These millions of migrants from rural areas have relocated at great cost – to themselves, their children and their communities. But they are driven by the new economics of China, in which staying home can seem even more costly.

This commentary originally appeared on The New York Times’ Opinion Pages as part of a Room for Debate series, “Life in a Mobile Nation”.