Neighborhoods matter. That’s the upshot of two fascinating new studies from Harvard economist Raj Chetty and his colleagues. In the 1990s, the federal government launched an experiment, called the Moving to Opportunity project. It created a lottery for housing vouchers that would allow the winners to move out of high-poverty neighborhoods into low-poverty ones. The project’s initial findings were a disappointment for people — like me — who argue that culture matters quite a lot. It did find that neighborhood poverty was a big factor in determining economic mobility, but researchers saw little evidence that getting poor people out of...