After 30 years, one of America's most intractable social problems is finally turning around: Overall homelessness has fallen 12 percent since 2005. Thanks goes to a eureka insight, followed by a coordinated nationwide push. The progress proves that Americans at all levels can tackle difficult challenges if they commit to them.

The light-bulb idea is pretty intuitive, though it took decades to settle on it: Instead of merely managing the homeless – shuttling them between shelters, detox centers, hospitals, and jails – local officials now work to first give them a long-term residence. Case workers then make sure they get the services they need, and that they don't again end up on the street.

The concept, known as "housing first," has been mostly directed at the chronically homeless, a term the federal government defines as mentally ill or otherwise disabled people who have been without a residence for at least a year, or who have been homeless several times over several years.

From 2005 to 2007, the number of chronically homeless fell 30 percent, to 123,833, according to a Department of Housing and Urban Development (HUD) report last month. The overall number of homeless fell to about 672,000 people. (Merely counting the homeless is quite a feat.)

Congress began to push "housing first" in 1999 by ordering HUD to funnel a third of its homeless funds into permanent housing. Then, under President Bush, HUD began to provide incentive money to communities that focus on the chronically homeless. Now there are 345 such communities – local governments, charities, and businesses – working with 10-year plans to reduce or end homelessness.

But what's progress without the critics, or the reminder that there's much more to do?

Some advocates for the homeless complain that HUD's numbers are not an apples-to-apples comparison, because the agency narrowed its definition of the homeless in the time covered. HUD itself admits to "large" sampling errors.

Maybe the real picture is not as "wow" as it appears, but the important thing here is that the trend is downward – and solutions are at hand.

A more legitimate complaint is that HUD is focusing too heavily on the chronically homeless, who make up about 18 percent of the homeless population. In New York City, for instance, this group has declined since 2005, but overall homelessness has increased.

The HUD report also covers a period mostly in advance of the fallout from the spike in housing foreclosures. Anecdotes from shelters and food pantries indicate the mortgage crisis and its attendant high rents are now being felt, with families one of the fastest growing homeless groups.

HUD had a good reason to focus on those who keep circulating through shelters. They're the most expensive and difficult group to take care of – especially if they remain on the street. Local governments can make substantial savings by stopping this cycle, and cities such as Denver are proving that.

But it's time now to apply the lessons of "housing first" to families and the working poor. Government can learn from its mistakes. It did this with welfare reform in the 1990s, and it's doing it now with the homeless.