What's the best way to provide opportunity?

Good profile of economist Raj Chetty who finds that housing vouchers which allow poor families to move to "opportunity" neighborhoods, help younger kids catch up to richer peers.  President Trump signed a bill that uses the research to guide policy:

Tenants have just started moving, but the program is already successful: The majority of families who received assistance moved to high-opportunity areas, compared with one-fifth for the control group, which was not provided with the extra services. Chetty estimates that the program will increase each child’s lifetime earnings by $88,000. In February, President Donald Trump signed into law a bill that provides $28 million to try similar experimental programs in other locations. 

However, Chetty still doesn't know what makes neighborhoods better:

For example, the strongest correlation is the number of intact families. The explanation seems obvious: A second parent usually means higher family income as well as more stability, a broader social network, additional emotional support, and many other intangibles. Yet children’s upward mobility was strongly correlated with two-parent families only in the neighborhood, not necessarily in their home. There are so many things the data might be trying to say. Maybe fathers in a neighborhood serve as mentors and role models? Or maybe there is no causal connection at all. Perhaps, for example, places with strong church communities help kids while also fostering strong marriages. The same kinds of questions flow from every correlation; each one may mean many things. What is cause, what is effect, and what are we missing? 

HT:  MarginalRevolution.com