For decades, communities across the USA have tried all manner of raising high school graduation rates: higher academic standards, better school funding, stricter testing and calls for arts, vocational, Advanced Placement and International Baccalaureate programs.

New research suggests there’s another way to raise graduation rates: simply increase the number of adults in a community.

Combining decennial U.S. Census and education data, a pair of researchers has found that improving the ratio of adults aged 25+ to school-aged children helps keep…