From a recent Raj Chetty study:
The number one factor that decreases mobility is single motherhood, even living with two parents in a community of many single mothers. Fascinating.
2. Economic (Racial?) Segregation – I put racial with a question mark as I do not know if there is an added racial component on top of the economic one. That is, is the Bronx (well mixed hispanic and black) better than east new york (all black)? In cities with a poor white population (mostly in the south), is this a factor?
3. School Quality
4. Social Capital – this seems like the likely channel where living in a community with many single mothers causes harm. (h/t Reihan).
Note that income inequality is no longer significant if the other 4 factors have been controlled for. The largest causes of inequality would likely be factors 1-3 so this is far from surprising.