For years, no one measured whether summer jobs programs actually achieved what city halls simply presumed they achieved. Rigorous examination of those claims was hampered by the time it would take to dig through the records from the nonprofits and private companies that provided the jobs, says Alicia Modestino, a labor economist at Northeastern University.

But over the past few years, academic studies, many connected to MIT’s Abdul Latif Jameel Poverty Action Lab, have started to tally results, in some cases tracking outcomes of summer jobs programs through randomized controlled trials.

The results have been surprising. Things long assumed to be true have been proven false, while other unanticipated, but hugely consequential benefits have been revealed.

Here are six things city governments need to know, based on several groundbreaking deep dives on summer jobs programs in New York (65,000 kids), Boston (3,300) and Chicago (31,000).