One of the strangest things about social policy in this country is that we know what works and yet don't do more of it. Take high-school dropout rates, which currently stand at roughly 50 percent for Latino and African-American males. The half who don't graduate (about a million kids a year) are often dooming themselves to a Hobbesian life that is "nasty, brutish and short." The wasted human potential is dooming the United States to second-class status as a global economic power.

We all know that the trouble starts early, with bored, unsupervised kids hanging out after school—the time when most crimes by young people are committed. Nearly 600,000 black males are currently serving time in prison, while only 40,000 will earn a college degree. Murders committed by black male teenagers are up 52 percent since 2002, which doesn't take us back to the bad old days of crack in the 1990s but is scary all the same.

Thousands of commendable small programs try to address this problem, but only one has achieved the scale to actually dent it. It's an institution you've heard of but probably know little about—in part because its facilities nowadays are only in the worst neighborhoods, a good hike from affluent areas. Last week I heard Denzel Washington and Cuba Gooding Jr. talk about how it changed their lives, and the same goes for Colin Powell, Wesley Clark, Michael Jordan and Alex Rodriguez.

The 101-year-old Boys and Girls Clubs of America is an astonishing success story, second only to the black church as a source of stability in the inner city. It has more than doubled in size in the last decade, to 3,700 clubs in all 50 states (including 400 clubs in public housing projects and 200 on Native American reservations), serving 4.4 million young people after school. That's still less than a third of the estimated 15 million at-risk youth, but it's a model that actually holds the potential to end this national shame—if we as a country could only focus on it.

In case you haven't been in one for a while, these clubs are about a lot more than sports. In fact, Shaquille O'Neal recently donated $1 million with the stipulation that it not go for basketball, since, as he put it, there are only 400 jobs to aspire to in his line of work. The funds will instead be devoted in part to Project Learn, which engages kids between six and 18 in academically beneficial club activities that are also (usually) fun, helps them with their homework and guides them to graduation.

Denzel Washington told a story that stuck with me. He was about eight or nine years old and attending a club in Mount Vernon, N.Y., when a local politician came to visit. The young Denzel asked the politician a question, and afterward an adult from the club told him, "Hey, you're smart." He was stunned: "This was a totally new concept to me, that I could do something in the world." Washington remembers a few years later looking up at the pennants from all the universities attended by alumni of that club and thinking for the first time that he might actually go to college.