Island School is one of 247 “community schools” in New York. These are regular public schools, with a twist. They have longer days and longer school years: Island stays open 12 hours a day, six days a week, including spring and winter breaks as well as the summer.

Some places lift children out of poverty. Others trap them there. Now cities are trying to do something about the difference.

A body of evidence points to a link between living in areas of concentrated poverty and health.