More than 150,000 U.S. families are homeless each year. The number has been going down, in part because of a program known as rapid rehousing, which quickly moves families out of shelters and into homes. But new research by the Obama administration finds that for many families, rapid rehousing is only a temporary fix.

It seemed like a good idea back in 2009 — when the recession had pushed thousands of families into homelessness. Rather than stay in shelters, families would get rental assistance for a few months — maybe a year — until they could get back on their feet. "What rapid rehousing did is say from the moment a family walks in, how can we get you out of here as quickly as possible and back into a home of your own," says Jennifer Ho, a senior adviser on housing and services at the U.S. Department of Housing and Urban Development. As part of the Economic Recovery Act, Congress approved about $1.5 billion for the program, making it a key tool for reducing family homelessness.

But Ho says new research by HUD has raised some red flags. "Rapid rehousing is not a magic solution," she says. Her agency has found that families that get rapid rehousing are just as likely later on to face the same housing problems as families that stay in shelters: Many of them end up returning to a homeless shelter, doubling up with family and friends or moving from place to place.